Chapter 39 Neural Signaling and Chapter 40 Neural Regulation

Chapter 39 Neural Signaling and Chapter 40 Neural Regulation

The Nervous System

Parts of a Neuron

• Receive stimuli• Produce and transmit electrical signals ( aka

nerve impulses/action potentials)• Synthesize and release neurotransmitters• Draw neuron• Many axons make nerve• Tracts/pathways – bundles of axons in CNS• Ganglia – groups of cell bodies outside CNS• Nuclei – groups of cell bodies inside CNS

Fig. 48-12

Axon

Schwanncell

Myelin sheathNodes ofRanvier

Node of Ranvier

Schwanncell

Nucleus ofSchwann cell

Layers of myelinAxon

0.1 µm

Neural Signaling: 4 processes(communication among neurons)

• Reception– Detect a stimulus– Neurons and sense organs

• Transmission– Message sent along neuron, between neurons, to

effector• Integration

– Sort and interpret incoming info, determine response• Action by effectors

– Actual response to stimulus

Fig. 48-3

Sensor

Sensory input

Integration

Effector

Motor output

Peripheral nervoussystem (PNS)

Central nervoussystem (CNS)

Types of Neurons

• Sensory neurons aka Afferent neurons– Info TO CNS

• Interneurons aka Association neurons– Info from afferent neurons to interneurons– Integrate and output– Most common– Cell body and axon in CNS

• Motor neurons aka Efferent neurons– Carries message from CNS to effector

Glial Cells (neuroglia)– support and protect neurons, regulatory functions - CNS

• Microglia– Phagocytes – remove debris

• Astrocytes– Star-shaped– Provide glucose to neurons– Regulate extracellular fluid

• Oligodendrocytes– Form sheath of myelin around neurons

• Schwann cells– Outside of CNS– Form sheaths around some axons

Fig. 49-6

Oligodendrocyte

Microglialcell

Schwann cells

Ependy-malcell

Neuron Astrocyte

CNS PNS

Capillary

(a) Glia in vertebrates

(b) Astrocytes (LM)

VENTRICLE

50 µ

m

• Nerve impulse• Myelin• Multiple sclerosis

Synapses

• Presynaptic neuron / Postsynaptic neuron• Electrical synapse• Chemical synapse

Electrical synapse

• 2 neurons very close together • Interiors of 2 cells physically connected by

protein channel• Ion passage between cells, permitting an

impulse to be directly and rapidly transmitted from pre to postsynaptic neuron

• Used for escape responses

Chemical synapse

• More common• 2 neurons separated by synaptic cleft• Depolarization of property of PM so when

action potential reaches end of axon it is unable to jump the gap

• Electrical signal must be converted to chemical signal (neurotransmitter)

• When postsynaptic neuron reaches threshold depolarization, it transmits an action potential

Fig. 48-15

Voltage-gatedCa2+ channel

Ca2+12

3

4

Synapticcleft

Ligand-gatedion channels

Postsynapticmembrane

Presynapticmembrane

Synaptic vesiclescontainingneurotransmitter

5

6

K+Na+

• Neurotransmitter – conduct neural signal across synapse and bind to chemically activated ion channels in PM of postsynaptic neuron– Ex: acetycholine– Norepinephrine, serotonin, dopamine

• Neuromodulator – messengers that modify the effects of specific neurotransmitters– Some amplify/dampen response by postsynaptic cell

How Neurotransmitters (NT) work

• Stored in synaptic terminals in synaptic vesicles• Action potential reaches synaptic terminal• Voltage-gated calcium channels open• Calcium ions from extracellular fluid flow into

synaptic terminal• Ca ions cause synaptic vesicles to fuse with

presynaptic membrane and release NT into synaptic cleft by exocytosis

• NT diffuse across synaptic cleft and combine with specific receptors on dendrites or cell bodies of postsynaptic neurons (or PM of effector cells)

• Ligand-gated ion channel – NT receptor, chemically activated

• Ligand (NT) binds with receptor and ion channel opens

• Ex: Ach receptor is ion channel for passage of Na+ and K+

Resting Potential VideoAction Potential Video

Synapse Video

Repolarization - Quick

• Excess NT must be removed• Degraded by enzymes

– Ex: Acetylcholinesterase breaks Ach choline + acetate

• Active transport back into synaptic terminal = reuptake– Repackaged and recycled

Drugs inhibit reuptake

• Antidepressants• SSRIs – selective serotonin reuptake inhibitors

– Fluoxetine (Prozac)• Cocaine - dopamine

NT – different effects with different neurons

• Ach– Excite – skeletal muscle– Inhibit – cardiac muscle

• Excitatory postsynaptic potential (EPSP)– Change in membrane potential that brings neuron

closer to firing• Inhibitory postsynaptic potential (IPSP)

– Change in membrane potential that takes the neuron farther away from firing

How Neurons WorkVideo

Chapter 40: Neural Regulation

• Vertebrate Nervous System• CNS

– Complex brain continuous with spinal cord– Central control– Integrate incoming info– Determine appropriate response

• PNS– Sensory receptors and nerves (communication lines)

Fig. 49-4Peripheral nervoussystem (PNS)

Cranialnerves

Brain

Central nervoussystem (CNS)

GangliaoutsideCNS

Spinalnerves

Spinal cord

Fig. 49-5

Whitematter

Ventricles

Gray matter

• Cranial nerves– Link body parts to brain

• Spinal nerves– Link body parts to spinal cord

Vertebrate Brain• Brainstem = medulla, pons, midbrain

– Medulla• Most posterior• Regulate respiration, heartbeat, BP, swallowing, coughing,

vomiting– Pons

• Mammals• Bulge anterior of brain stem• Bridge – connects spinal cord and medulla with upper

parts of brain• Regular respiration• Relay impulses from cerebrum cerebellum

Fig. 49-UN1

– midbrain• (mesencephalon)• Visual reflexes (pupil constriction)• Auditory reflexes• Muscle tone and posture

• Cerebellum– Muscle activity – tone, posture, equilibrium

(balance)• Thalamus

– Relay center for motor and sensory messages

• Hypothalamus – Below thalamus– Olfactory centers– Principal integration center for regulation of viscera– Provides input to medulla and spinal cord that

regulate heart rate, respiration, digestive function– Controls body temp.– Regulates appetite, water balance– Emotional/sexual responses– Links nervous and endocrine systems, produces

certain hormones

• Cerebrum– Most prominent– Olfactory– R and L hemispheres– Mostly white matter (mainly myelinated axons that

connect various parts of brain)– Surface convolutions = numerous folds

• Expands surface• Sulci – furrows between convolutions if shallow• Fissures if deep

– # folds associated with complexity of brain function

– Gray matter – cerebral cortex• Makes up outer portion of cerebrum• Contains cell bodies and dendrites

Human CNS

• Well-protected brain and spinal cord• 3 layers connective tissue (meninges) and

encased in bone• 3 meningeal layers

– Outer dura mater– Middle arachnoid– Thin vascular pia mater (adheres closely to tissue

of brain and spinal cord)

• Meningitis – disease where these coverings become infected and inflamed

• Cerebrospinal fluid (CSF)– Between arachnoid and pia mater, in subarachnoid space– Produced by choroid plexus = special networks of

capillaries extend up from pia mater into brain ventricles; extract nutrients from blood and adds them to CSF

– Choroid plexus and arachnoid serve as barrier between blood and CSF (prevent harmful substances from entering the brain)

• CSF– Shock absorber– Cushions brain and spinal cord– Medium for exchange of nutrients and waste

products between brain and blood

Spinal Cord

• Base of brain to L2 vertebra• Central canal surrounded by gray matter (cell

bodies, dendrites, unmyelinated axons, glial cells) in “H” shape

• White matter (outside gray matter) of myelinated axons in bundles (tracts)

Reflex action

• Relatively fixed response pattern to a simple stimulus

• Predictable, automatic, unconscious• Ex: breathing

Withdrawal reflex

• Touch hot stove, jerk hand away• Route of the message

– Pain receptor in skin sensory neuron spinal cord association neuron appropriate motor neuron group of muscles

• Same time – message sent to conscious areas of brain (up spinal cord)– Aware, feel pain (not part of reflex)

Fig. 49-3

Whitematter

Cell body ofsensory neuron indorsal rootganglion

Spinal cord(cross section)

Graymatter

Hamstringmuscle

Quadricepsmuscle

Sensory neuronMotor neuronInterneuron

Human Cerebrum

• Cerebral cortex (outer part of cerebrum)• R and L cerebral hemispheres• Functionally divided into 3 area

– 1 – sensory – receive incoming signal from sense organs

– 2 – motor – control voluntary movement– 3 – association – link sensory and motor areas,

responsible for thought, learning, language, memory, judgment, personality

• Occipital lobes – vision• Temporal lobes – hearing• Central sulcus – groove across top of each

hemisphere from medial to lateral edge– Partially separate frontal lobes from parietal lobes

• frontal lobes – skeletal muscles• Parietal lobes – heat, cold, touch, pressure

from skin

Fig. 49-15

Speech

Occipital lobe

Vision

Temporal lobe

Frontal lobe Parietal lobe

Somatosensoryassociationarea

Frontalassociationarea

Visualassociationarea

ReadingTaste

Hearing

Auditoryassociationarea

Speech

Smell

Mot

or c

orte

xSo

mat

osen

sory

cor

tex

• Size of motor area in brain for a given body part proportional to complexity of movement involved– Ex: hands and face = large areas

• One side of brain controls opposite side of body

• Uppermost part of cortex controls lower limbs of body

• White matter of cerebrum under cerebral cortex

• Nerve fibers of white matter connect the cortical areas with 1 another and with other parts of the nervous system

• Corpus callosum - Large band of white matter, connects R and L hemispheres

• Basal ganglia– Deep in white matter– Paired groups of nuclei (gray matter)– Coordination and movement– Send signals to midbrain

• Cerebral cortex – integrates info about diverse activities– Arousal, sleep, emotion, information processing

The Brain and Sleep-wake

• “brain waves” / electrical potentials generated by active neurons can be measured

• Recorded by electroencephalogram (EEG)• Electrodes taped to scalp and activity of

cerebral cortex measured

• Alpha waves– Most regular indication of activity– Occur rhythmically ~ 10/sec.– Mostly from visual areas in occipital lobe (rest quietly,

eyes closed)• Beta waves

– Rapid, irregular waves, eyes open– Fast frequency – Heightened mental activity

• Delta and theta waves– Slow, large waves associated with certain stages of

sleep

Fig. 49-11

High-frequency waves characteristic of wakefulness

Lefthemisphere

Key

Time: 0 hours

Low-frequency waves characteristic of sleep

Righthemisphere

Location Time: 1 hour

• Learning– Process by which we acquire info as a result of

experience• Memory

– Process by which information is encoded, stored, retrieved

Peripheral Nervous System

• Consists of sensory receptors, nerves linking receptors with CNS, nerves linking CNS with effectors

• Somatic system (of PNS)– Helps body response to changes in external

environment– Maintain body’s posture and balance– Cranial nerves – 12 pairs

• Emerge from brain• Smell, sight, hearing, taste

Fig. 49-7-2

Efferentneurons

Locomotion

Motorsystem

Autonomicnervous system

Afferent(sensory) neurons

PNS

Hearing

CirculationGas exchange DigestionHormone

action

Entericdivision

Sympatheticdivision

Parasympatheticdivision

– Spinal nerves – 31 pairs• Emerge from spinal cord• Named for general region of vertebral column from

which they originate• 8 pairs cervical• 12 pairs thoracic• 5 pairs lumbar• 5 pairs sacral• 1 pair coccygeal• Each one has dorsal root and ventral root

– Dorsal root• Info from sensory receptors to spinal cord

– Ventral root• Info leaves spinal cord to muscles and glands

• Autonomic system– Helps maintain homeostasis in internal

environment– Regulates heart rate, maintain constant body

temp.– Works automatically, involuntary– Effectors = smooth and cardiac muscle, glands– Functionally organized into reflex pathways– Receptors in viscera relay info to CNS

• Efferent portion of autonomic system (away from CNS)– Sympathetic and parasympathetic

• Opposite effects• Ex: heart rate sped up – sympathetic• Heart rate slowed – parasympathetic• Sympathetic – stimulates organs, mobilize energy• Parasympathetic – conserve and restore energy

• Autonomic– Preganglionic neuron

• 1st neuron• Has cell body and dendrites in CNS• Axon (peripheral nerve) ends by synapsing with a

– Postganglionic neuron• Dendrites and cell body are in ganglion outside CNS• Axon terminates near/on effector