Anatomy & Physiology 12 Name: Ms. Hansen The NERVOUS SYSTEM 12.1 Nervous Tissue Function: Consists of: Central Nervous System (CNS): Peripheral Nervous System (PNS): The Nervous system contains 2 types of cells: Neurons and Neuroglia Neurons between parts of the nervous system Neuroglial cells , maintain homeostasis and form Neurons have 3 parts; dendrite, cell body, axon Dendrite - carries the nerve impulse Cell body - contains the of the cell which maintains cell function Axon - carries the action potential the cell body towards another or an Sensory neuron May have specialized endings called which detect changes in the environment and carry the message to the CNS.
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The NERVOUS SYSTEM · 2019-12-05 · 12.2 Transmission of nerve impulses A nerve impulse is also called an When the neuron is not firing, it has a of ~ mV. Action potential A rapid
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Anatomy & Physiology 12 Name:
Ms. Hansen
The NERVOUS SYSTEM
12.1 Nervous Tissue
Function:
Consists of:
Central Nervous System (CNS):
Peripheral Nervous System (PNS):
The Nervous system contains 2 types of cells: Neurons and Neuroglia
Neurons between parts of the
nervous system
Neuroglial cells
, maintain homeostasis and form
Neurons have 3 parts; dendrite, cell body, axon
Dendrite - carries the nerve impulse
Cell body - contains the of the cell which maintains cell function
Axon - carries the action potential the cell body towards another
or an
Sensory neuron
May have specialized endings called which detect changes in the
environment and carry the message to the CNS.
Interneuron
Receives messages from other interneurons,
received and communicate with
Motor neuron
Carry the message from the to an (muscle, organ or glands)
Myelin Sheath
Some axons are covered in a protective myelin sheath to
and aid in nerve regeneration.
Myelin is a type of lipid found in the membranes of
(neuroglia in the PNS) or (neuroglia in the CNS)
Nodes of Ranvier: gaps between Myelin Sheath (allows for ~200m/s transmission) (without:
5m/s) “Saltatory conduction”
Tracts: bundles of myelinated axons in CNS (white matter)
Nerves: bundles of myelinated axons in PNS
12.2 Transmission of nerve impulses
A nerve impulse is also called an
When the neuron is not firing, it has a of ~ mV.
Action potential
A rapid change in polarity across an axonal membrane
As the action potential moves through the neuron, the same
three steps occur;
1. Depolarization
open
Sodium ions move
Sodium gates close
2. Repolarization
open
Potassium ion diffuse of the neuron
Potassium gates close
3. Refractory period
The ions are on the wrong side of the membrane
The restores the previous ion
distribution by moving 3 sodium out and 2 potassium in.
Anatomy & Physiology 12 Name:
Ms. Hansen
The Synapse
A synapse is a region where the axon of one neuron is in
to the cell body or dendrite of another
are used to carry the action potential across
the synaptic cleft
Process of transmission
1. The nerve impulse reaches and
cause gates to open (instead of Na+)
2. Calcium ions diffuse into the neuron and interact with the contractile
proteins that causes the (containing the neurotransmitters) to with
the presynaptic membrane
3. The neurotransmitters are released into the synaptic cleft ( ).
4. The neurotransmitters across the synaptic cleft to (on Na+
channels) on the post synaptic membrane (dendrite or cell body of the next neuron)
5. Depending on the type of NT and receptor, this alters the potential of the post synaptic membrane
either in an or manner.
Excitatory signals have a depolarizing effect causing the membrane potential to move
closer to threshold. Inhibitory signals have the opposite effect
6. The neurotransmitters are then either by the presynaptic membrane or
by enzymes in the synaptic cleft
Neurotransmitters
There are at least 25 different NT’s identified
Examples: Acetylcholine (ACh) and Norepinephrine (NE)
Specific enzymes are present in the post synaptic membrane to break down these NT’s
o i.e. Acetylecholinesterase (AChE)
Synaptic integration
A neuron has many synapses. It also has a threshold that must be
reached in order for it to fire.
Excitatory NTs cause the neuron to get closer to its threshold. (open
Na+ channels)
Inhibitory NTs cause the neuron to get further away from the threshold
(may open K+ or Cl- channels K+ out or Cl- in = hyperpolarization)
There could be up to 200 synapses on a post synaptic neuron. Each
synapse may be contributing excitatory or inhibitory NTs.
The combination of excitatory and inhibitory NTs must be enough to
reach the threshold
Size of the action potential
The size of the action potential produced in a neuron Is
. You can tell a strong
stimulus (knife cut) from a weaker stimulus (pin prick) in two
ways
o for the
strong stimulus
o The neurons will fire for the
stronger stimulus
Synapses in drugs (research)
Anatomy & Physiology 12 Name:
Ms. Hansen
The Central nervous system
Composed of the and
Protected by
o Bone: Scull and vertebrae
o 3 tough layers of membrane
o
found between the meninges, in the central canal and in
the ventricles of the brain
cushions the brain and the spinal cord
o Spinal cord leaves skull through
Spinal cord
Structure:
Grey matter:
White matter (myelinated) : bundled together in
o Ascending tracts
o Descending tracts
Function:
Grey matter:
o Ex: Reflex arc
White matter:
o Ex: Receptors in skin send message through sensory neurons to spinal cord, up ascending
tracts to brain, brain sends message down descending tracts in spinal cord then through
motor neurons to effector.
The Brain
4 Main parts
1.
2.
3.
4.
Cerebrum
Largest part of the brain
The outer surface of grey matter is called the . This area accounts for
and
Its divided into the left and right hemispheres by the .
Each hemisphere has 4 lobes; the Frontal, Parietal, Occipital and Temporal lobes.
Cerebral cortex
Somatosensory cortex receives information from your body
Motor cortex sends information out
Frontal lobe
Primary motor cortex control voluntary
Association (premotor) areas organize complex motor activities
Processing center: Prefrontal area allows humans to
and formulate ,
Broca’s area is associated in refining grammar/
Parietal lobe
Primary somatosensory cortex
(touch, temperature, pain)
Somatosensory association area analyzes information from
the skin and muscles
Occipital lobe
Dedicated to
Visual association area compares new images with old images to
determine if there are any relationships
Temporal lobe
Primary auditory area receives information from
Auditory association area is used to match new sounds with