Physbrain

NEUROPHYSIOLOGY

Dr. Steven Resnick, D.O.

Neurology Resident

Jackson Memorial Hospital

LECTURE OUTLINE• I INTRO - OVERVIEW OF THE

NERVOUS SYSTEM• II NEURON• III ACTION POTENTIAL• IV SYNAPSE• V BRAIN• VI SPINAL CORD• VII AUTONOMIC NERVOUS SYSTEM• VIII CRANIAL NERVES• IX CONCLUSION

Basic Functions of the Nervous System

• Sensory Function– Detection of both internal and external stimuli

• Interpretive Function– Analyzes, stores, and makes decisions based on

sensory information

• Motor Function (Response)– Response to interpretive data

Nervous System

• Afferent (sensory) Neurons – Carry impulses toward the CNS

• Efferent (Motor) Neurons – Carry impulses from the CNS

• Interneurons – conduct impulses within the spinal cord (between afferent and efferent) (Syn. Association, Internuncial)

• Ganglia are small masses of nervous tissue located outside the brain and spinal cord.

Fine Anatomy of the Nervous SystemThree kinds of neurons:

– Sensory

– Motor

– Interneurons

Neurons

Sensory Motor Interneurons

1) Sensory: Sensory organs to CNS“Receptors”

2) Motor: CNS to muscles and organs“Effectors”

3) Interneurons: Connections within CNS“Processors”

Sensory Neurons

• INPUT From sensory organs to the brain and spinal cord.

Somatosensory neuron - spinalVision, hearing, taste and smell -

cranial

SpinalCord

BrainSensoryNeuron

Touch receptors in skin

Motor Neurons

• OUTPUT From the brain and spinal cord to muscles and glands

SpinalCord

Brain

MotorNeuron

Motor neurons in spinal cord

Interneurons

• PROCESSING Relay information between other neurons

SpinalCord

Brain

Inter-Neurons

Interneurons in brain

General Organisation of the Nervous System

The Nervous System

Central Nervous System Peripheral Nervous System

Brain Spinal Cord Somatic Autonomic

Sensory MotorParasympathetic

Sympathetic

The Nervous System

• Two subsystems– Central nervous system (CNS)

• Brain and Spinal Cord– Integrate, correlate, and respond to many different kinds

of sensory information

– Source of thoughts, emotions, and memories

– Peripheral nervous system (PNS)• Includes all nervous tissue outside of the CNS

– Cranial nerves, spinal nerves, etc.

Divisions of the PNS

• Somatic Nervous System (SNS)– Sensory neurons that convey information from

sensory receptors in the head, body wall and limbs to the CNS

– Motor neurons from the CNS that conduct impulses to the skeletal (voluntary) muscles only.

Divisions of the PNS

• Autonomic Nervous System (ANS)– The motor portion of the ANS consists of two

divisions• Sympathetic (thoracolumbar region)

– Fight/flight (prepares the body to cope with stressful situations)

• Parasympathetic (craniosacral region)– Rest/Repose (generally an opposite response to the

sympathetic nervous system)

Divisions of the PNS

• Autonomic Nervous System (ANS)– Sensory neurons convey information from

receptors in the viscera (internal organs), to the CNS.

– Motor neurons then convey information from the CNS to smooth muscle, cardiac muscle, glands, etc.

– Motor functions in the ANS are not normally under conscious control; they are involuntary.

{sensorysensory

motormotor

autonomicautonomicnervousnervoussystemsystem

{somaticsomaticnervousnervoussystemsystem{somaticsomaticnervousnervoussystemsystem

{brainbrain

spinalspinalcordcord

{afferentafferentnervesnerves

efferentefferentnervesnerves{

parasympatheticparasympatheticnervous systemnervous system

sympatheticsympatheticnervous systemnervous system

peripheral nervousperipheral nervoussystem (PNS)system (PNS)

nervousnervoussystemsystem

central nervouscentral nervoussystem (CNS)system (CNS)

Major Divisions of the Nervous SystemMajor Divisions of the Nervous SystemMajor Divisions of the Nervous SystemMajor Divisions of the Nervous System

Peripheral Nervous System:Afferent and Efferent Neurons

Neurons

– “Functional unit” of nervous system

– Several Types– Conduct nerve

impulses– Electrical excitability – Structures

• Cell body• Axon• Dendrites

The Nerve Cell Body

• An enlarged part of the nerve cell containing abundant cytoplasm and cell organelles. It is sometimes called the soma.

• Receives information from dendrites and sends messages out through the axon.

• The primary site for maintaining the life of the nerve cell which support the dendrites and axon.

Nervous Tissue

• Cell body– Nucleus surrounded by

cytoplasm

– Contain organelles such as lysosomes, mitochondria, Golgi complexes, and rough ER (Nissl bodies) for protein production.

– No mitotic apparatus

The Dendrite

• An incoming nerve cell process that can act as a receptor or connect to separate specialized receptors.

• Conducts stimulus information to the nerve cell body.

• Produces voltage changes in response to various stimuli and assists in nerve impulse formation.

Nervous Tissue

• Dendrites (little trees)

– Receiving end of the neuron

– Conduct impulses toward the cell body

– Short and highly branched

– Also contain organelles

The Axon Hillock

• The junction site between the nerve cell body and the axon.

• Processes voltage changes , or generator potentials (GP’s) from the cell body and dendrites, and assists the formation of a transmittable nerve impulse.

The Axon

• Conducts nerve impulses away from the nerve cell to the axon terminals.

• Is very small in diameter, but can be very long (e.g. the length of a leg).

• Each nerve cell has only one axon.

• If an axon is cut, the distal portion degenerates due a disruption of the cytoplasm extending from the cell body.

Axon

• Conducts impulses away from the cell body toward another neuron, muscle fiber or gland cell.

• Also contains organelles

• “Axon hillock – where the axon joins the cell body.

• The “initial segment” is the beginning of the axon.

• The “trigger zone” is the junction between the axon hillock and the initial segment.

Axon Terminals

• Axon terminals are bulbous distal endings of the many branches that extend from the end of an axon. These bulb-like structures can also be called synaptic knobs, boutons or even “end feet”.

• The axon terminal serves as a secretory component that releases neurotransmitters in response to nerve impulses.

Nervous Tissue

• Axon Terminals– Site of communication

between two neurons or between a neuron and an effector cell.

Representative neuronin

out

Soma

“cell body”

Neuron thatDelivers signalTo the synapse

Region where anAxon termimalMeets its targetCell

The cell thatReceives thesignal

Nervous Tissue (2 Types)

• Neuroglia = “glue” • Smaller than neurons but more numerous

• Do not generate or conduct nerve impulses

• Support neurons

• Form myelin sheath

• Participate in phagocytosis

Neuroglia• CNS

– Astrocytes-maintain chemical environment (Ca & K) - Blood Brain Barrier

– Oligodendrocytes-produce myelin in CNS – Microglia-participate in phagocytosis – Epedymal cells-form and circulate CSF

• PNS– Schwann cells-produces myelin in PNS – Satellite cells-support neurons in PNS

Astrocytes:NutrientTake up K+ And Neuro-TransmittersFrom ECF

GLIAL CELLS OF THE CNS

GLIAL CELLS OF THE CNS

Ependymal Cells:Epithelial CellsCreate SelectivelyPermeable BarrierBetween CompartmentsOf the Brain

GLIAL CELLS OF THE CNS

Oligodendrocytes:Support andInsulate axonsBy creating myelin

In CNS, oneOligodentrocyteForms myelinAround portions ofSeveral Axons

Glial Cells• Peripheral nervous system:

– Schwann cells: produce myelin sheath of peripheral nerve fibers; wrap around the axon**spaces between adjacent sections of myelin where the axon’s plasma membrane is exposed to extracellular frluid are the Nodes of Ranvier.

Each Schwann cell associates with a single axon.– Satellite cells:nonmyelinating Schwann cell: Form

supportive capsules around nerve cell bodies that are located in the ganglia, outside the CNS

The Schwann Cell

• A specialized cell that supports and maintains the fibers (axons and dendrites) of nerve cells in the peripheral nervous system (PNS). Contains myelin material.

• Assists the in repair and regeneration of fibers.

• Wraps around a section of a nerve fiber and creates a protective myelin sheath.

Nodes of Ranvier

• A Node of Ranvier is a space or gap found on a nerve cell process (axon or dendrite) and is located between the myelin sheaths formed by cells such as the Schwann Cell.

• The exposed cell membrane located in the node can facilitate the formation and transmission of nerve impulses.

The Myelin Sheath

• The Schwann Cell wraps around a section of nerve cell fiber in “jellyroll”fashion resulting in a tight coil of concentric membranes called the Myelin Sheath.

• The whitish, fatty myelin material acts as an excellent insulator and protector of the nerve cell fiber.

Myelin Sheath

– Cover for a nerve fiber– Lipid (white matter) and

Protein– Insulates and increases

impulse speed– Formed by Schwann cell

membranes (PNS)– Oligodendrocytes (CNS)

• Multiple Sclerosis– Autoimmune destruction

of myelin sheaths

The Neurilemma

• The most external portion of the plasma or cell membrane of the Schwann Cell.

• This specialized membrane surrounds the myelin sheath.

• The neurilemma is sometimes called the sheath of the Schwann Cell or a neuron “husk”.

Myelination

• 1 mm in length• Up to 100 layers• Neurolemma (sheath of Schwann) assists with regeneration of

damaged neurons

Nerve Tissue Regeneration

• At birth, the cell bodies of neurons lose their mitotic features (Can not be replaced by daughter cells)

• To regenerate, neurons must:– Be myelinated– Have intact cell body– Have functional Schwann cells

Regeneration

• Wallerian Degeneration is anterograde degeneration characterized by the disappearance of axons and myelin sheaths and secondary proliferation of Schwann cells (occurs in CNS and PNS)

• Chromatolysis- the result of retrograde degeneratin in the neurons of the CNS and PNS.

Regeneration

• CNS- Effective regeneration does not occur in the CNS. For examaple, there is no regeneration of the optic nerve or no basement membrane/endoneural surrounding the axons of the CNS

• PNS- Regeneration does not occur in the PNS. The proximal tip of a severed axon grows into the endoneural tube which consists of Schwann basement membrane and endonerium.

Nerve Tissue Regeneration

The axons sprout grows at the rate of 3 mm/day

Nerve Tissue Regeneration

• Axons in the CNS do not form neurilemmas, so they do not survive axonal damage.

• Damaged Neurons in the CNS are also rapidly converted to scar tissue (proliferation of astrocytes)

ACTION POTENTIAL• Nerve signals are transmitted by action

potentials that are abrupt, pulse-like changes in the membrane potential that last a few ten thousandths of a second.

• Action potentials can be divided into three phases: the resting or polarized state, depolarization, and repolarization

• The amplitude of an action potential is nearly constant and is not related to the size of the stimulus, so action potentials are all-or-nothing events.

ACTION POTENTIAL

• Cell membranes of excitable tissue, including neurons, contain ion channels that are responsible for generating action potentials

• These membrane channels are guarded by voltage-dependent gates that open and close with change in the membrane potential

• There are separate voltage-gated channels for the sodium., potassium, and calcium channels.

Membrane potential• 2 factors influence membrane potential:

• 1.) Concentration gradients of different ions across the membrane

• 2.) The permeability of the membrane to these ions

Cell Membrane in resting state

K+

Na+ Cl-K+A-

Outside of Cell

Inside of Cell

Na+ Cl-

Ionic Concentration Gradients

0 mV

RESTING MEMBRANE POTENTIAL

• Approximately -70mV, cell negative

• is the result of the high resting conductance to K+, which drives the membrane potential toward the K+ equilibrium potential

• At rest, the Na+, channels are closed and Na+ conductance is low

Cell Membrane at rest

Na+ Cl-K+

Na+

Cl-K+ A-

Outside of Cell

Inside of Cell

Potassium (K+) can pass through open channels to equilibrate its concentration

Sodium and Chlorine cannot pass through

Result - inside is negative relative to outside

- 70 mV

The Resting Potential: Ionic Gradients & a Semi-Permeable Membrane

Resting Potential

ACTION POTENTIAL

• • K+ is high inside so increased K+ permeability causes more K+ to leave cell (inside becomes negative).

• Na+ is high outside so increased Na+ permeability causes more Na+ to enter cell (inside becomes positive).

• Membrane potential is a compromise based on which ion is more permanent

UPSTROKE OF A.P.1) Inward current depolarizes the membrane

potential to threshold

2) Depolarization causes rapid opening of the activation gates of the Na channel, and the Na+ conductance of the membrane promptly increases.

3) The Na+ conductance becomes higher than the K conductance and so the membrane potential is driven toward the Na+ equilibrium potential of +65 mV

** The rapid depolarization during the upstroke is caused by an inward NA+ current

REPOLARIZATION OF A.P.• Depolarization also closes the inactivation gates of

the Na+ channel (more slowly than it opens the activation gates). Closure of the inactivation gates means that the Na+ channels close, and so Na+ conductance returns toward zero

• Depolarization slowly opens K+ channels and increases K+ conductance to even higher levels that at rest.

• The combined effect of closing the Na channels and greater opening of the K channels makes the K conductance higher than the Na conductance and the membrane potential is repolarized.

** Repolarization is caused by an outward K current

Action potential initiation

S.I.Z.

Action potential terminationThink

“votes”

Positive feedback loop

Reach “threshold”?

If YES, then...

Action Potential

Absolute Refractory Period.• Is the period during which another action

potential cannot be elicited no matter how large the stimulus

• coincides with almost the entire duration of the action potential

• Explanation: the inactivation gates of the Na channel are closed and will remain closed until repolarization occurs. No action potential can occur until the inactivation gates open.

Relative refractory period• Begins at the end of the absolute refractory

period and continues until the membrane potential returns to the resting level

• An action potential can be elicited during this period if a stronger than usual current is provided

• Explanation: The K+ conductance is higher than at rest, the membrane potential is closer to the K equilibrium potential and farther away for threshold; more current is required to bring the membrane to threshold.

Refractory periods

Saltatory Conduction• Propagation of action potentials occurs by spread of local currents to adjacent areas of membrane, which are then depolarized to threshold and generate action potentials.

• Conduction velocity is increased by:

1) increasing diameter of a verve fiber resuts in decreased internal resistance and so conduction velocity down the nerve is faster

2) Myelination. Myelin acts as an insulator around nerve axons and increases conduction velocity. Myelinated nerve exhibits saltatory conduction because action potentials can be generated only at the nodes of Ranvier, where there are gaps in the myelin sheath.

Saltatory Conduction

Terminology

• Synapse– Region at which neurons come nearly together to

communicate. (neuron or effector organ)

• Synaptic Cleft– Gap between neurons (at a synapse)

– Impulses can not propagate across a cleft

• Synaptic Vesicle– Packets of neurotransmitter in presynaptic neuron

Terminology

• Presynaptic Neuron– Neuron sending a signal (before the synapse)

• Postsynaptic Neuron– Neuron receiving a signal (after the synapse)

• Neurotransmitter– Substance that tends to cause excitement– Required to transmit impulses across a synaptic

cleft

Direction of chemical synapse

• One Direction– Synaptic vesicles are only located in the pre-

synaptic nerve ending. – Only the post-synaptic neuron contains

receptors for the neurotransmitters

Chemical Synapses• An action potential in the presynaptic cell

causes depolarization of the presynaptic terminal

• As a result of the depolarization, Ca enters the presynaptic terminal Ca entry causes release of neurotransmitter in the presynaptic cleft

• Neurotransmitter diffuse across the synaptic cleft and combines with receptors on the postsynaptic cell membrane, causing a change in its permeablilty to ions and its membrane potential.

Syn

apti

c P

hysi

olog

y

Locks and Keys• Neurotransmitter

molecules have specific shapes

positive ions (NA+ ) depolarize the neuron negative ions (CL-) hyperpolarize

When NT binds to receptor, ions enter

Receptor molecules have binding sites

Synaptic transmission• Excitatory postsynaptic potentials(EPSP)/

Inhibitory postsynaptic potentials (IPSP) are inputs that depolarize/heperpolarize the postsynaptic cell bringing it closer/away from firing an action potential

• EPSP are cause by opening of channels that are permeable to Na and K

Neurotransmitters :Ach, NE, Epinephrine, dopamine, serotonin

• IPSP are cause by opening Cl channels

Neurotransmitters: GABA and glycine

Postsynaptic Inhibition

IPSP

EPSP

Types of Neurotransmitters• Acetylcholine

• Serotonin

• Norepinephrine

• Dopamine

• Endorphins

• GABA

• Glutamate

Acetylcholine

• Found at neuro-muscular junction– Involved in muscle

movements (nicotine, curare)

• In CNS: recticular activating system– Slow excitation of cerebral

neurons (muscarine, atropine)– Memory

Neuromuscular Junction

• Is the synapse between axons of motorneurons and skeletal muscle. The neurotransmitter released from the presynaptic terminal Ach, and the receptor on the postsynaptic membrane is nicotinic

Neuromuscular Junction and Ach

1. Synthesis and storage of Ach in the presynpatic terminal

choline acetylransferase catalyzes the formation from acetyl coA and choline in the presynaptic terminal.

2. Depolarization of the presynaptic terminal and Ca uptake

3. Calcium uptake causes release of Ach into the synaptic cleft

4. Diffusion of Ach to the poststnaptic membrane (muscle end-plate) and binding to specific receptors

5. depolarization of adjacent membrane to threshold

6. Degradation of Ach to acetyl CoA and choline by acetylcholinesterase (acheE) on the muscle end plate

Myasthenia gravis• Is characterized by skeletal muscle

weakness and fatigability resulting from a reduced number of Ach receptors on the muscle end plate ( due to autoimmune antibodies against acetylcholine receptors at the neuromusclar juntion

• Diagnosis and treatment involves Acetylchlinesterase inhibitors (neostigmine)- prolong the action of Ach at the muscle end plate.

Synaptic Function - Drug Effects• 1) Release Inhibitors - ex: Botulinum toxin (in botulism)

• 2) Acetylcholinesterase Inhibitors - ex: Nerve Gas

• 3) Postsynaptic Blockers - ex: Curare and most Snake venoms

• 4) Sodium Channel Blockers - ex: Pufferfish venom and red tide toxins

Serotonin• Involved in mood, depression

– Prozac works by blocking reuptake– Ecstasy (MDMA) kills 5-HT terminals in

forebrain, releasing massive amounts

• Pain regulation (descending brainstem)

• Involved in regulation of cortical activity (sleep?)

Dopamine

• Involved in movement, attention, learning, motivation, reward

• Overactive dopamine:– Schizophrenia

• Underactive (loss of) dopamine:– Parkinson’s Disease

• Loss of dopamine neurons in the substantia nigra

• Symptoms:– difficulty starting/stopping voluntary movements– tremors at rest– stooped posture– rigidity– poor balance

Parkinson’s Disease

• Main inhibitory neurotransmitter in CNS

• Benzodiazepines (Valium) and alcohol agonise GABA receptor complexes

• Also some anti-epileptic drugs

Gamma-Aminobutyric Acid (GABA)

Huntington’s Chorea• Involves loss of neurons in

striatum that utilize GABA

• Symptoms:– jerky involuntary movements– mental deterioration

Central Nervous System• Cerebral ganglia (brain)

• Spinal Cord

dorsalcaudal orposterior

rostral oranterior

ventraldorsal

neuraxisdorsal

ventral

lateralmedialmedial

lateral

dorsallateralmedialmedial

lateral

ventral

caudal orposterior

caudal orposterior

dorsalvent

ral

rostral oranterior

neuraxis

Basic DirectionsBasic DirectionsBasic DirectionsBasic Directions

Basic DirectionsBasic DirectionsBasic DirectionsBasic Directions

dorsal

ventraldorsal

ventral

caudal

caudal

rostral

rostraldorsal

ventral

coronal plane(frontal or coronal section)

horizontal ortransverse plane

coronal plane(cross section)

sagittal plane

Basic DirectionsBasic DirectionsBasic DirectionsBasic Directions

X

FIGURES 4.3 & 4.4 on FIGURES 4.3 & 4.4 on pgs. 90-91pgs. 90-91

dorsal

ventral

CNS - The REAL Forebrain

This is Your Brain

• 1.5kg of water, lipids and protein contained in your cranium

• The most important and complex organ in your body

• 100 billion neurons• 100 million billion

connections between neurons

Top Bottom

Side Middle

6 Major Regions of the Brain

• 1.) Cerebrum

• 2.) Diencephalon

• 3.) Midbrain

• 4.) Pons

• 5.) Cerebellum

• 6.) Medulla Oblongata

Brain• White matter

– Mostly axons– Myelin sheaths– Bundles of axons that connect different regions

of the CNS are TRACTS

• Gray Matter:– Unmyelinated– Dendrites, Axon terminals

• Ascending tracts= carry sensory information from cord to the brain

• Descending tracts = carry efferent (motor) signals from brain to cord

Functions of Brain Structures

• Sulcus ----------- A depression or groove in the surface of the cerebrum that helps increase surface area of the

cerebrum.

• Gyrus ------------ An elevated ridge that projects upwards between the sulci of the cerebrum and also helps

increase surface area of the cerebrum..

• Central Sulcus ------- a deep groove that serves as a dividing line between the frontal and

parietal lobe.

The Lobes of the CortexThe Lobes of the CortexThe Lobes of the CortexThe Lobes of the Cortex

Functions of Brain Structures Continued:

• Frontal Lobe ----- controls conscious muscle action, planning for movements, motor memory, voluntary eye movements.

• Parietal Lobe ----- Controls conscious interpretation of sensation from muscles, tongue and cutaneous areas.

• Temporal Lobe --- conscious interpretation of auditory and olfactory sensations. Memory of sounds and smells.

• Occipital Lobe ------- the most posterior lobe of the cerebrum which deals with conscious seeing, eye focus and integrating visual memory with other sensations.

Cerebrum

Lobes of the Cerebrum

• Frontal Lobe-voluntary and involuntary control of skeletal muscles, speaking & writing

• Parietal Lobe-general sensations• Temporal Lobe-sound and smell• Occipital lobe-sight• All Lobes-Memory, emotions, reasoning, and intelligence

Function of Brain Structures Continued

• Cerebral Cortex ----- the outer layer of the cerebrum that consists of gray matter which deals with conscious motor action, sensation, memory, communication, reasoning, emotions, intelligence

• Sensory Area of the Cerebral Cortex -- Located in areas posterior to the central sulcus. Receives and

interprets conscious sensory impulses. The postcentral gyrus of the parietal lobe is a key ridge of gray matter that allows a person to judge the source of sensory stimuli.

• Motor Area of the Cerebral Cortex --- Located in areas anterior to the central sulcus. Plans and initiates impulses for conscious motor movements. The precentral gyrus of the frontal lobe is a another key ridge of gray matter that allows a person to operate specific areas of the body.

(Parietal)

Brain Parts

Cerebrum

• Left and Right

cerebral Hemispheres

• Connected at the Corpus Callosum

Cerebrum• Corpus

Callosum– Transverse

fibers of white matter that connects the cerebral hemispheres

Cerebral Cortex• Thick blanket of neural cortex

• Covers the cerebrum

• Outer surface:– Series of elevated ridges or gyri separated by

shallow depressions called sulci, or deeper grooves called fissures

Cerebrum• Cortex

– Superficial layer of gray matter (6 layers)

Cerebrum• Gyrus (gyri)

(Convolutions)

– Out-folds or ridges in the gray matter

– Gray matter grows faster that white during development

Cerebrum• Sulcus

– Shallow grooves in gray matter

• Fissure– Deep grooves– The “longitudinal

fissure” separates left and right hemispheres (halves)

– Transverse fissure separates the cerebrum from the cerebellum

Hemispheric Lateralization (split-brain)

• The two hemispheres of the brain share performance of many functions but they also specialize in performing certain unique functions.

• Left hemisphere– Language, numerical and scientific skills, reasoning,

control of right-side skeletal muscles

• Right hemisphere– Musical and artistic awareness, perception, recognition,

emotional content of language, mental imaging from sound, touch, taste, smell, and control of left-side skeletal muscles

Cerebral Lateralization• Language/Verbal = left

Dominant for Right handed people

Spatial Skills = Right

• Right hemisphere = synthesis

• E.G., drawing, map reading, perception, recognition

Damage to Cerebral Cortex• Damage to primary somatic sensory cortex

= reduced sensitivity of the skin on the opposite side of the body

• Damage to primary motor cortices= frontal lobes = skeletal muscle and voluntary movementExample: StrokeParalysis of the opposite side occurs

Cerebrum• Interior of cerebrum contains 3 clusters of

cell bodies:• 1.) Basal ganglia = corpus striatum

– Control of movement

• 2.) Amygdala = emotion and memory• 3.) Hippocampus = learning and memory

Basal Ganglia (Cerebral Nuclei)• Masses of gray matter located mainly in each hemisphere

that control gross, unconscious movements of skeletal muscles. (swing arms while walking, talking with your hands, etc.)

Thalamus• The thalamus functions a relay station for

all sensory impulses (except smell-hypothalamus) to the cerebral cortex.

• The thalamus also functions as a center for impulses such as pain, temperature, and crude touch and pressure.

Limbic System• Region of the cerebrum that surrounds the

brain stem

• Includes several groups of neurons- limbic cortex-cingulate gyrus, parahippocampal gyrus, uncus and associated subcortical strucures- thalamus, hypothalamus, amygdala

Limbic System• Also includes centers within the

hypothalamus responsible for:– 1.) emotional states—rage, fear, and sexual

arousal– 2.) control of reflexes that can be consciously

activated like chewing, licking, and swallowing

Limbic System

Brain Parts• Cerebellum

– “Little Brain”

– Inferior to cerebrum

– Posterior to brain stem

– Separated from the cerebrum by the transverse fissure

Cerebellum• Subconscious level

• Adjusts postural muscles, maintains balance and equilibrium

• Coordinates complex movements

Similarities of the Cerebellum and Cerebrum

• Two hemispheres

• Lobes

• Sulci, fissures, and convolutions (folia)

• Gray matter cortex

• White matter (cerebellar nuclei)

Functions of the Cerebellum

• Coordination

• Posture

• Proprioception – Awareness of movement, equilibrium and

position

• Balance

Cerebellum

Brain Parts• Brain Stem

(3 parts)– Superior to

the spinal cord

– Midbrain

– Pons

– Medulla Oblongta (medulla)

Brain Stem• Contains important processing centers and

relay stations for information passing from or to cerebrum or cerebellum and controls vital functions such as breathing and digestive activities

Functions of Brain Structures Continued• Medulla Oblongata ------ The most inferior part of the

brain stem which relays information between the spinal cord, the pons and cerebellum. The medulla also contains control centers for regulating “ vital signs” such heart rate, blood pressure and primary respiration rate.

• Pons -------------- A part of the brain stem that serves as a relay between the medulla oblongata, cerebellum and the midbrain. The pons also contains the pneumotaxic and apneustic center for secondary control of breathing.

• Midbrain ------------------- A central section in the brain interior that is located between the pons and

thalamus. This brain region is the most superior part of the brain stem and contains visual reflex centers, auditory reflex centers and motor control centers (e.g. substantia nigra

Medulla• Medulla has two external bulges called the

pyramids.The pyramids are formed by the largest motor tracts.

• Axons from the left pyramid cross over to the right and axons on the right cross over to the left. (Decussation of Pyramids)– Left hemisphere of brain controls right side muscles;

right hemisphere controls left side.– Lateral to each pyramid is an oval-shaped swelling

called an “olive”. The swelling is caused by the “inferior olivary nucleus”. They carry signals from proprioceptors in muscles to the cerebellum.

Medulla• Contains reflex centers that function in

regulating– Heartbeat, force of cardiac contraction,

diameter of blood vessels (Cardiovascular center), rhythm of breathing, and reflex centers for vomiting, coughing, and sneezing.

• Controls input and output of 5 of 12 cranial nerves (VIII, IX, X, XI, XII)

Pons• Lies directly above the medulla and anterior to

the cerebellum (2.5 cm).• Bridge connecting the spinal cord with the brain

and parts of the brain with each other. • Together with the medulla, areas in the pons help

control breathing.• Origin of 4 cranial nerves (V, VI, VII, VIII)

– Chewing, head and face sensations, certain eyeball movements, taste, salivation, facial expression, and equilibrium

Midbrain• Extends from the pons to the diencephalon (2.5

cm).• The cerebral aqueduct passes through the

midbrain thereby connecting the third and fourth ventricles.

• Reflex center for eyes, head, and neck• Origin of 2 cranial nerves (III, IV)

Oxygen And Glucose Requirements Of The Brain

• The brain is very active and uses about 20% of the total oxygen supply in the body.

• The primary nutrient of the brain is glucose. Glucose is broken down aerobically in presence of the abundant brain oxygen supply in order to yield large quantities of ATP.

External Support For Nervous Tissue

• BONE Casing:

Skull or cranium –brain

Vertebral column – spinal cord

Brain Structure Functions Continued

• Gray Matter ---------- Dark tissue of the brain made up of cell bodies and nuclei.

• White Matter --------- Light tissue of the brain made up of myelinated nerve cell processes (dendrites and axons).

• Dura Mater ------------ The tough, outermost meningeal membrane that covers and protects the

surface of the brain and spinal cord (“the tough mother membrane”).

• Arachnoid Mater ------ The middle meningeal membrane that contains web-like spaces for storing and

circulating CSF (“the spider web membrane”).

Brain Structure Functions Continued

• Pia Mater -------------- The innermost meningeal membrane that covers the surface of the brain and spinal cord in a very close, protective fashion (“the gentle mother membrane”).

• Association Areas ----- Regions of the cerebral cortex that analyze, recognize and act on sensory input and

communicate with the motor areas. Examples include the visual and auditory association areas.

External Support For Nervous Tissue

• Between bones and tissue of the CNS: three layers of connective tissue membrane: meninges– 1.) dura mater: forms the outermost covering

of the CNS. Inner and outer layers are separated by an area of loose connective tissue that contains tissue fluids and blood vessels

External Support for Nervous Tissue

• 2.) Arachnoid membrane: Spidery web of collagen and elastic fibers that fills the underlying subarachnoid space. The subarachnoid space is filled with cerebrospinal fluid.

External Support for Nervous Tissue

• 3.) pia mater: below the subarachnoid space is the innermost meningeal layer. This layer is firmly attached to the neural tissue of the CNS, supports the blood vessels serving the brain, and spinal cord.

Brain Structure Functions Continued

• Ventricles ----------------------- Hollow spaces in the brain which store cerebral spinal fluid ( CSF ) for support, protection and circulation of extracellular fluid (ECF).

• Cerebral Spinal Fluid ( CSF ) - A specialized extracellular fluid produced by choroid plexi which bathes, supports and protects the interior of the brain and spinal cord.

• Choroid Plexus ------------------ A cluster of specialized capillaries enclosed by specialized cells that line the brain ventricles. These circulatory bodies produce cerebral spinal fluid ( CSF ).

External Support for Nervous Tissue

• Cerebrospinal Fluid (CSF)

• Salty solution continuously secreted into ventricles (hollow cavities) of the brain

CSF• 1.) Physical protection

• 2.) Regulate extracellular fluid environment:– Concenctrations of K+, Ca+, HCO3-, and

glucose are lower, and H+ is higher in CSF as compared to plasma

– CSF contains very little protein, and no blood cells

Composition of CSF vs Plasma

Substance Plasma CSF

Protein mg/dl 7500 20

Na (Meq/L) 145 141

Cl- 101 124

K+ 4.5 2.9

HCO3 25 24

pH 7.4 7.32

Glucose (mg/dl) 92.0 61.0

Ventricles

• Fluid filled cavities within the brain

2 lateral ventricles, one in each cerebral Hemisphere; no direct connection betweenThe 2, but both open into the third ventricle of The diencephalon

Midbrain has a slender canal known as the cerebralAqueduct which connects the third ventricle with the Fourth ventricle of the pons and superior portionOf the medulla oblongata

Within the medulla oblongata the fourth ventricleNarrows and joins the central canal of the spinal cord

Choroid Plexus• Choroid plexus: specialized tissue found on the

walls of the ventriclesSecretes CSFConsists of capillaries and transporting epithelium: EpendymaEpendyma actively pump Na and other solutes into the ventricles, creating an osmotic gradient that draws water into the ventricles

CNS - Flow of CSF in CNS1) Choroid Plexus makes CSF in Lateral Ventricle

2) CSF moves around fornix3) Joins fluids from choroid plexus in 3rd Ventricle4) Down cerebral aqueduct5) Joins 4th Ventricle fluids from choroid plexus6) Leaves aperatures or goes down central canal in spine7) Circulates in arachnoid8) Reabsorbed into blood of dural sinus by arachnoid villi

Arachnoid Villi• CSF is gradually reabsorbed

into the blood through the arachnoid villi (finger-like projections that project into the dural sinuses) example: superior sagital sinus

• 20 mL/hr reabsorption rate• Pressure remains constant

because reabsorption and formation rates are the same.