Nervous System
1. Sensory input.
2. Integration.
3. Homeostasis.
4. Mental activity.
5. Control of skeletal muscles.
The Nervous System
Organization of the Nervous
• Central nervous system (CNS)
– Brain and spinal cord
• Peripheral nervous system (PNS)
– Neurons outside the CNS
– Sensory division
• Afferent fibers transmit impulses from receptors to CNS
– Motor division
• Efferent fibers transmit impulses from CNS to effector organs
Relationship between motor and sensory fibers of the
PNS and the CNS
Autonomic Nervous System
• Sympathetic
– Fight or flight, stress
– Excitatory effects elicited by norepinephrine
activating beta receptors
– Inhibitory effects elicited by activation of alpha
• Parasympathetic
– Rest and digest
– Digestive system activated, heart rate inhibited,
blood vessels dilated
– Vagus nerve primarily responsible for
activating parasympathetic responses
Fig. 8.39
Specialized site of intercellular communication.
3 Components:
1. Presynaptic terminal
2. Synaptic cleft
3. Postsynaptic membrane
Functional Organization of the
Nervous System
The Neuron
• Accessory cells of the nervous system
• Astrocytes
– Support tissue in the CNS form blood-brain barrier
• Ependymal
– Produce and move cerebral spinal fluid
• Microglia
– Remove cell debris and bacteria from CNS
• Oligodendricytes and Schwann cells
– Provide insulation around axons of CNS and PNS
Myelinated vs. Unmyelinated
Membrane Potentials
• Nervous system functions by establishing
concentration gradients and electrical
potentials across the membranes
• The resting membrane potential of a neuron
is negative and is said to be polarized
• These gradients are maintained by the
sodium potassium pump
Concentration Gradients and Nerve
Cell Function
Action Potentials
• Muscle and nerve cells are exciteable
• When a muscle or nerve cell is stimulated Na+
channels open and Na+ rushes into the cell
• This causes a local potential
• This local potential may not result in action
– Doesn’t cross the threshold
• If the stimulus is sufficient to cause the local
potential to cross the threshold an action
potential results
• The action potential is the complete
depolarization of the cell
• The action potential is an all-or-nothing event
– If the local potential meets threshold, the cell totally
depolarizes and the action potential results
– If the potential does not meet threshold, no action
potential results
Fig. 8.9
Fig. 8.10
Action Potential Propogation
• Unmyelinated neurons propogate signals
more slowly than myelinated neurons
• Myelination acts as an insulator
– Electrical signal will jump from node of
Ranvier to node of Ranvier
– This is called saltatory conduction
– Requires less energy than direct propogation
Propagation of the Action Potential
• Electrical
• Chemical
--communication occurs in one direction:
presynaptic membrane to postsynaptic
--action potential is not always propagated.
Synapses may occur:
• neuron to neuron
• neuron to another type of cell (neuroeffector)
--neuromuscular junction
--neuroglandular junction
The Synapse
Fig. 8.13
--packaged in synaptic vesicles.
Nerve endings of the ANS secrete:
• Acetylcholine (ACh)--Cholinergic neuron
– Parasympathetic effector
• Norepinephrine (NE)--Adrenergic neuron
– Sympathetic effector
• Neurotransmitters diffuse across the
synaptic cleft and bind to receptor on the
post-synaptic membrane
• This can cause membrane channels (Na+,
K+, or Cl-) to open or close depending on
the neurotransmitter
• If stimulatory, Na+ channels will open
• If inhibitory, K+ or Cl- channels will open
– Cell becomes more negative, hyperpolarized
2 types of cholinergic receptors:
• Nicotinic
– Preganglionic sympathetic and parasympathetic
• Muscarinic
– parasympathetic
2 types of adrenergic receptors:
• Alpha
– Generally inhibitory
• Beta
– Generally excitatory
Autonomic Reflex Arc
Sensory neuron
Association neuron
Autonomic motor neuron
Visceral effector
Reflex Arc
Knee Jerk Reflex
Converging Circuit
Central Nervous System
• Brainstem
--medulla oblongata
• Diencephalon
• Cerebrum
• Cerebellum
• Medulla oblongata
– Inferior portion
– Regulation of heart rate, venoconstriction,
ventilation, swallowing, , etc..
• Pons
– Superior to medulla
– Bridge between cerebrum and cerebellum
• Midbrain
– Audio and visual processing
• Integrates motor signals from cerebral
cortex with feedback from PNS
• Proprioception
• Learning tasks
• Thalamus
– Sensory input from PNS passes through
thalamus (relay station)
• Epithalamus
– Pineal gland – sleep cycle, puberty
• Hypothalamus
– Master gland
– Attached to pituitary by infundibulum
– Controls much of homeostasis by stimulating or
inhibiting pituitary
Brain Protection:
cranial bones
cranial meninges
cerebrospinal fluid
The Brain
• Largest part of the brain; thinking part
• Markings:
Gyrus (gyri)-- wrinkle, raised area
Fissure(s)-deep, wide groove(s)
Sulcus (sulci)-- shallow groove(s)
1) Frontal
2) Parietal
3) Temporal
4) Insular
5) Occipital
Displays lateralization:
• left hemisphere
language; math/science; reason
• right hemisphere
music/art; spatial relations;
• sensory areas
• motor areas
• association areas
Spinal Cord-- Composition
white matter (myelin)
dorsal column
ventral column
lateral column
gray matter (non-myelin)
posterior horn
ventral horn
lateral horn
Spinal Cord-- White Matter
• myelinated axons that travel along the spinal cord.
Ascending-- up cord to higher levels
Descending-- down cord from brain
Across the cord
Spinal Cord
• Dorsal roots (sensory)
• Ventral roots (motor)
combine to form spinal nerve.
• Dorsal Root Ganglion
Peripheral Nervous System
Cranial Nerves
• 12 pr.-- I to XII (anterior to posterior)
3 functions:
1) sensory
2) somatic-- control of skeletal muscle
3) parasympathetic--regulation of glands,
smooth muscle, and cardiac muscle.
Peripheral Nervous System
Spinal Nerves
• 31 pr. 8 cervical
12 thoracic
5 lumbar
5 sacral
1 coccygeal
rootlets  roots  spinal nerve  ramus
Dorsal rami
Ventral rami-Distributed 2 Ways:
Intercostal nerves (T1-T12)
Plexuses (5):
cervical plexus (C1-C5)
brachial plexus (C5-T1)
lumbar plexus (L1-L4)
sacral plexus (L4-S4)
coccygeal plexus (S4, S5, Cx)

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