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Overview of the nervous system

FLG 327: Lecture 1
by

Evangeline Nortje

on 17 August 2016

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Transcript of Overview of the nervous system

Cells of the nervous system
Neurons
peripheral
nervous system

Neural reflexes
Overview of neurophysiology
Organization of the nervous system
Autonomic Nervous System
CNS
PNS
Afferent division
somatic sensory
visceral sensory
special sensory
Efferent division
somatic motor
autonomic motor
sympathetic
parasympathetic
brain
spinal cord
Neuroglia
signaling units
of the nervous system

support cells
of the nervous system

Parts of a neuron
Cell body
Dendrites
Axon
Presynaptic
axon terminal

Postsynaptic
dendrite

Input
signal

Integration

Output
signal

synaptic cleft
Synapse:
The region where an axon terminal communicates with its postsynaptic target cell

Postsynaptic neuron

Presynaptic neuron
functional & structural categorisation
Functional categorisation
sensory neurons
Interneurons of CNS
Efferent neuron
Structural categorisation
Pseudounipolar
Bipolar
Anaxonic
Multipolar
Support cells of the CNS
Glial cells
don't participate
directly in transmission of electrical signals
They support neurons
physically
,
metabolically
, and
functionally
interaction: neurons & glial cells
Myelination
glial cell wraps around the axon
each wrap becomes 2 membrane layers

Deflated balloon wrapped tightly
around a pencil

Electrophysiology
of nerve cells
Nerve cell
= excitable tissue
propagate electrical signals rapidly in response to a stimulus
Neurons have a RMP of –70 mV
Changes in membrane potential...
graded potentials
action potentials
sub-threshold
A graded potential starts above threshold (T) at its initiation point
but
decreases in strength as it travels through the cell body
At the trigger zone, it is below threshold and therefore does not initiate an action potential
Suprathreshold
A stronger stimulus at the same point on the cell body ..
creates a graded potential that is still above threshold ...
by the time it reaches the trigger zone
an action potential results
Resting membrane potential
Depolarizing stimulus
Membrane depolarizes to threshold. Voltage-gated Na+ and K+ channels begin to open.
Rapid Na+ entry depolarizes cell.
Na+ channels close and slower K+ channels open.
K+ moves from cell to extracellular fluid.

K+ channels remain open and additional K+ leaves cell, hyperpolarizing it.
Voltage-gated K+ channels close, less K+ leaks out of the cell.
Cell returns to resting ion permeability and resting membrane potential.
Synaptic transmission
Classified as
electrical
or
chemical
depending on
signal
passing from pre- to postsynaptic cell
Electrical synapses
pass electrical signals through gap junctions
Chemical synapses
Chemical synapses use neurotransmitters that cross synaptic clefts
efferent division that controls the response
somatic reflexes
autonomic reflexes
CNS location where reflex is integrated

spinal reflexes
cranial reflexes
the time at which the reflex develops
innate reflex
conditioned reflex
the number of neurons in the reflex pathway
Monosynaptic reflex
Polysynaptic reflex
31 pairs of spinal nerves
8
12
5
5
1
each spinal nerve contains
afferent
&
efferent
fibres
segment of spinal cord showing pair of nerves
ventral root
carries
efferent
(motor) information
dorsal root
carries
afferent
(sensory) information
anatomy of PNS in region of spinal nerve
12 pairs of cranial nerves
originate from brain stem
Some cranial nerves include purely sensory OR motor fibres
Some cranial nerves contain motor AND sensory fibres (mixed nerves)
sympathetic
Most internal organs are under antagonistic control
excitatory
vs
inhibitory

parasympathetic
Point of origin in CNS
Thoracolumbar outflow:
Anatomy
Location of peripheral ganglia
T1 - L2
originate in thoracic & lumbar regions of spinal cord
primarily in ganglion chains close to vertebral column
paravertebral sympathetic chain
Neuron length
Short pre- & long postganglionic neurons
Point of origin in CNS
Craniosacral outflow:
Anatomy
Location of peripheral ganglia
CN III, VI, IX, X
&
S2 - S4
originate mostly from brainstem & sacral region
located on or near target organs
Neuron length
Long pre- & short postganglionic neurons
NTM's released
Preganglionic
neurons release:
Postganglionic
neurons release:
acetylcholine (Ach)
norepinephrine (NE)
NTM's released
Preganglionic
neurons release:
Postganglionic
neurons release:
acetylcholine (Ach)
Receptors
Ganglionic synapse:
Neuron-target
synapse:
nicotinic cholinergic (nAChR)
adrenergic receptors
(α ; β)
Receptors
Ganglionic synapse:
Neuron-target
synapse:
nicotinic cholinergic (nAChR)
acetylcholine (Ach)
muscarinic cholinergic (mAChR)
Comparison
sympathetic
parasympathetic
long
short
long
short
CNS integrates sensory info
sensory info
spinal cord
brain
cranial nerves
reflex arc
brainstem
Special senses
Somatic senses
Motor pathways
pyramidal tract / corticospinal tract
direct pathway
indirect pathway
cerebral cortex
brain stem
spinal cord
basal ganglia
cerebellum
Supports muscle activities
Posture
Balance
Locomotion

fibres that end in brainstem =
corticobulbar tract
motor neurons involved in the CNS motor tracts
LMN axons leave the CNS and innervate skeletal muscles

motor pathways
the CNS integrates movement
somatic motor pathway
comparison of somatic motor & autonomic divisions
Spinal cord organization
Gray matter
White matter
Full transcript