nervous system functions: 1.sensory input. 2.integration. 3.homeostasis. 4.mental activity....
TRANSCRIPT
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Nervous System
FUNCTIONS:
1. Sensory input.
2. Integration.
3. Homeostasis.
4. Mental activity.
5. Control of skeletal muscles.
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The Nervous System
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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
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Relationship between motor and sensory fibers of the PNS and the CNS
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Autonomic Nervous System
• Sympathetic– Fight or flight, stress– Excitatory effects elicited by norepinephrine
activating beta receptors– Inhibitory effects elicited by activation of alpha
receptors
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• Parasympathetic– Rest and digest– Digestive system activated, heart rate inhibited,
blood vessels dilated– Vagus nerve primarily responsible for
activating parasympathetic responses
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Fig. 8.39
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Synapse
Specialized site of intercellular communication.
3 Components:
1. Presynaptic terminal
2. Synaptic cleft
3. Postsynaptic membrane
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Functional Organization of the Nervous System
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The Neuron
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Neuroglia
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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
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Myelinated vs. Unmyelinated Axons
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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
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Concentration Gradients and Nerve Cell Function
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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
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• 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
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Fig. 8.9
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Fig. 8.10
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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
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Propagation of the Action Potential
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Synapse
• Electrical --rare• Chemical
--communication occurs in one direction:
presynaptic membrane to postsynaptic membrane
--action potential is not always propagated.
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Synapse
Synapses may occur:• neuron to neuron• neuron to another type of cell (neuroeffector)
--neuromuscular junction
--neuroglandular junction
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Fig. 8.13The Synapse
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Neurotransmitters
--packaged in synaptic vesicles.
Nerve endings of the ANS secrete:• Acetylcholine (ACh)--Cholinergic neuron
– Parasympathetic effector
• Norepinephrine (NE)--Adrenergic neuron– Sympathetic effector
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• 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
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Receptors2 types of cholinergic receptors:• Nicotinic
– Preganglionic sympathetic and parasympathetic
• Muscarinic– parasympathetic
2 types of adrenergic receptors:• Alpha
– Generally inhibitory
• Beta– Generally excitatory
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Autonomic Reflex Arc
1. Receptor
2. Sensory neuron
3. Association neuron
4. Autonomic motor neuron
5. Visceral effector
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Reflex Arc
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Knee Jerk Reflex
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Converging Circuit
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Central Nervous System
Adult:• Brainstem
--medulla oblongata
--pons
--midbrain
• Diencephalon
--thalamus
--hypothalamus
--epithalamus
• Cerebrum
• Cerebellum
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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
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Cerebellum
• Integrates motor signals from cerebral cortex with feedback from PNS
• Proprioception
• Learning tasks
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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
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Cerebrum
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Brain Protection:
• cranial bones
• cranial meninges
• cerebrospinal fluid
• neuroglia (astrocytes)
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The Brain
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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)
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CEREBRUM
Lobes:
1) Frontal
2) Parietal
3) Temporal
4) Insular
5) Occipital
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CEREBRUM
Displays lateralization:
• left hemisphere
language; math/science; reason
• right hemisphere
music/art; spatial relations; insight/imagination
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CEREBRUM
• sensory areas
• motor areas
• association areas
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Spinal Cord-- Composition
white matter (myelin)
dorsal column
ventral column
lateral column
gray matter (non-myelin)
posterior horn
ventral horn
lateral horn
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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
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Spinal Cord
• Dorsal roots (sensory)
• Ventral roots (motor)
combine to form spinal nerve.
• Dorsal Root Ganglion
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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.
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Peripheral Nervous System
Spinal Nerves
• 31 pr. 8 cervical
12 thoracic
5 lumbar
5 sacral
1 coccygeal
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SPINAL NERVESrootlets 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)