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Nervous System
FUNCTIONS:
1. Sensory input.
2. Integration.
3. Homeostasis.
4. Mental activity.
5. Control of skeletal muscles.
The Nervous System
Organization of the Nervous
System
• 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
receptors
• Parasympathetic
– Rest and digest
– Digestive system activated, heart rate inhibited,
blood vessels dilated
– Vagus nerve primarily responsible for
activating parasympathetic responses
Fig. 8.39
Synapse
Specialized site of intercellular communication.
3 Components:
1. Presynaptic terminal
2. Synaptic cleft
3. Postsynaptic membrane
Functional Organization of the
Nervous System
The Neuron
Neuroglia
Neuroglia
• 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
neurons
Myelinated vs. Unmyelinated
Axons
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
potential
– 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
Synapse
• Electrical
• Chemical
--rare
--communication occurs in one direction:
presynaptic membrane to postsynaptic
membrane
--action potential is not always propagated.
Synapse
Synapses may occur:
• neuron to neuron
• neuron to another type of cell (neuroeffector)
--neuromuscular junction
--neuroglandular junction
The Synapse
Fig. 8.13
Neurotransmitters
--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
Receptors
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
1.
2.
3.
4.
5.
Receptor
Sensory neuron
Association neuron
Autonomic motor neuron
Visceral effector
Reflex Arc
Knee Jerk Reflex
Converging Circuit
Central Nervous System
Adult:
• Brainstem
--medulla oblongata
--pons
--midbrain
• Diencephalon
--thalamus
--hypothalamus
--epithalamus
• Cerebrum
• Cerebellum
Brainstem
• 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
Cerebellum
• Integrates motor signals from cerebral
cortex with feedback from PNS
• Proprioception
• Learning tasks
Dienchephalon
• 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
Cerebrum
Brain Protection:
•
•
•
•
cranial bones
cranial meninges
cerebrospinal fluid
neuroglia
(astrocytes)
The Brain
CEREBRUM
• Largest part of the brain; thinking part
• Markings:
Gyrus (gyri)-- wrinkle, raised area
Fissure(s)-deep, wide groove(s)
Sulcus (sulci)-- shallow groove(s)
CEREBRUM
Lobes:
1) Frontal
2) Parietal
3) Temporal
4) Insular
5) Occipital
CEREBRUM
Displays lateralization:
• left hemisphere
language; math/science; reason
• right hemisphere
music/art; spatial relations;
insight/imagination
CEREBRUM
• 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
SPINAL NERVES
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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