FUNCTIONS: 1. Sensory input.
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
Specialized site of intercellular communication.
3 Components: 1.
Presynaptic terminal 2.
Synaptic cleft Postsynaptic membrane
Functional Organization of the Nervous System
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
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 --rare --communication occurs in one direction: presynaptic membrane to postsynaptic membrane --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
• 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
2 types of cholinergic receptors: Nicotinic
Preganglionic sympathetic and parasympathetic Muscarinic
2 types of adrenergic receptors: Alpha
Generally inhibitory Beta
Autonomic Reflex Arc
Receptor Sensory neuron Association neuron Autonomic motor neuron Visceral effector
Knee Jerk Reflex
Central Nervous System
Adult: Brainstem --medulla oblongata --pons --midbrain Diencephalon --thalamus --hypothalamus --epithalamus
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
• • • •
cranial bones cranial meninges cerebrospinal fluid neuroglia (astrocytes)
Largest part of the brain; thinking part
Markings: Gyrus (gyri)-- wrinkle, raised area Fissure(s)- deep, wide groove(s) Sulcus (sulci)-- shallow groove(s)
Lobes: 1) Frontal 2) 3) Parietal Temporal 4) 5) Insular Occipital
Displays lateralization: left hemisphere language; math/science; reason
right hemisphere music/art; spatial relations; insight/imagination
• • •
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.
-- up cord to higher levels
-- down cord from brain
Across the 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
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)