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Chapter 8 Lecture Notes page 1 Chapter 8 - Nervous System A. the nervous system coordinates the activities of other organ systems 1. monitors internal and external conditions 2. stores and integrates information 3. coordinates the activity of effector organs B. nerve tissue = neurons + neuroglia (NOOR oh GLEE uh) 1. neurons conduct electrical and chemical signals a. basic structure cell body contains nucleus dendrites carry signal to cell body axon and collaterals carry signals to other cells synaptic terminals at ends of axon contain neurotransmitter myelin surrounds some axons nodes of Ranvier are gaps in myelin b. categories sensory neurons - take signals from receptors to CNS motor neurons - take signals from CNS to effector organs (muscle and glands) interneurons - about 99% of CNS; connect sensory and motor neurons BIOL 2404 Strong/Fall 2006 Chapter 8 Lecture Notes page 2 2. neuroglia protect and support the neurons a. astrocytes (ASS troe sites) - CNS - help maintain blood-brain barrier, form structural framework for repair b. oligodendrocytes (OH lih go DEN droe sites) - CNS - form myelin c. microglia (MY crow GLEE uh) - CNS - phagocytes d. ependymal (ep EN dih mull) - CNS - line cavities in CNS, help produce and move cerebrospinal fluid e. Schwann cells - PNS - form myelin 3. synapses are where neurons communicate with each other and other cells a. presynaptic neuron synaptic terminals contains neurotransmitters stored in vesicles b. synaptic cleft = small space between cells c. postsynaptic neuron membrane contains receptors for the neurotransmitters and gated ion channels that regulate the membrane potential 4. basic multi-neuronal structures gray matter consists mostly of cell bodies white matter consists mostly of myelinated axons cortex - thin layer of neuron cell bodies (gray matter) covering the outside of parts of the brain nucleus - clump of neuron cell bodies (gray matter) located in CNS tract - bundle of axons in CNS BIOL 2404 Strong/Fall 2006 Chapter 8 Lecture Notes page 3 ganglion/ganglia - clump of neuron cell bodies in PNS, surrounded by c.t. nerve - bundle of axons in PNS, surrounded by c.t. C. neurophysiology 1. action potential – a temporary change in the membrane potential of a neuron that acts as a signal neurons maintain a resting membrane potential, then use temporary changes in potential to send messages along their membranes and to other cells an action potential occurs when a small area of neuron membrane becomes permeable to Na Na enters the cell and reverses the membrane potential Na entry is automatically cut off and K exit occurs a millisecond later K exit returns the membrane to resting potential BIOL 2404 Strong/Fall 2006 Chapter 8 Lecture Notes page 4 2. propagation an action potential occurs in a very small area each action potential, unless it is blocked by nerve damage or drugs, causes a new action potential in the adjacent membrane this process repeats to the end of the axon at the synaptic terminal the action potential causes the release of neurotransmitter, allowing the signal to be sent on to the next cell 3. channels the ion channels that let Na into and K out of the cell are gated that means their opening is controlled by outside factors like changes in membrane potential (voltage), chemicals, or mechanical factors Na and K channels at a synapse are controlled by the neurotransmitter Na and K channels in the axon are controlled by changes in membrane potential BIOL 2404 Strong/Fall 2006 Chapter 8 Lecture Notes page 5 4. the sodium/potassium pump works constantly to maintain Na and K gradients so that whenever ion channels open there is enough Na or K to move across the membrane to generate a signal D. Organization of the nervous system central nervous system (CNS) = brain + spinal cord peripheral nervous system (PNS) = cranial + spinal nerves afferent/sensory efferent/motor somatic - skeletal muscle autonomic - cardiac m., smooth m., glands CNS PNS sensory motor somatic autonomic E. spinal cord, spinal nerves 1. functions of spinal cord a. pathway between body and brain b. integrates reflexes (automatic and unlearned responses to sensory information) c. contains complex patterns used in activities like walking and running 2. anatomy of the spinal cord a. gross length: foramen magnum to L2 below L2 spinal nerves form cauda equina BIOL 2404 Strong/Fall 2006 Chapter 8 Lecture Notes page 6 consists of columns of white and gray matter cervical and lumbar enlargements represent extra nerve tissue needed for handling sensory input from and motor control of limbs b. cross sectional central canal filled with CSF gray columns - cell bodies of neurons and glial cells posterior - sensory neurons lateral - autonomic motor neurons anterior - somatic motor neurons white columns - ascending sensory tracts and descending motor tracts anterior lateral posterior BIOL 2404 Strong/Fall 2006 Chapter 8 Lecture Notes page 7 3. anatomy of the spinal nerves spinal nerves carry information into and out of the spinal cord each nerve has a dorsal root and a ventral root dorsal root ganglion is in dorsal root and contains cell bodies of sensory neurons dorsal root carries sensory information into the spinal cord ventral root carries motor information from the spinal cord dorsal and ventral roots join just inside vertebrae to form spinal nerves spinal nerves leave through intervertebral foramina BIOL 2404 Strong/Fall 2006 Chapter 8 Lecture Notes page 8 F. the simplified brain 1. cerebrum a. functions: consciousness, thinking, planning, conscience, memory, control of complex movements, awareness, localization of sensory input, language b. structure left and right hemispheres lobes: frontal, parietal, temporal, occipital cortical functional areas: sensory - visual, auditory; somatic (primary) association - premotor cortex, prefrontal area motor - primary speech - Broca’s, Wernicke’s BIOL 2404 Strong/Fall 2006 Chapter 8 Lecture Notes page 9 c. components cortex - thin layer of gray matter; where most cerebral functions occur white matter - connects cortex to other parts of brain: corpus callosum connects left and right hemispheres basal nuclei - deep to white matter; subconscious control of skeletal muscle 2. diencephalon a. epithalamus - pineal gland b. thalamus - processes and screens sensory input to cerebrum c. hypothalamus - physical response to emotion, water balance, temperature control, food intake, hormone secretion, 3. brain stem - pathway between spinal cord and diencephalon a. midbrain - motor responses to visual and auditory input, controls level of consciousness b. pons - integrates cerebellum and brainstem, motor control centers c. medulla oblongata - cardiac and respiratory control centers 4. cerebellum - coordination of skeletal muscle, posture, balance 5. ventricles cavities lined with ependymal cells contain CSF connected to each other and subarachnoid space 2 lateral ventricles in the cerebral hemispheres interventricular foramina 3rd ventricle in diencephalon cerebral aqueduct BIOL 2404 Strong/Fall 2006 Chapter 8 Lecture Notes page 10 4th ventricle between brainstem and cerebellum 4th ventricle continuous with central canal of spinal cord 6. limbic system - structures in the cerebrum and diencephalon; emotional state, memory storage and retrieval G. protective systems of CNS 1. meninges (men IN gees) – singl. – meninx (MEN inks) 3 layers of c.t. surrounding brain and spinal cord continuous with coverings of nerves shock absorbing epidural space dura mater subdural space arachnoid subarachnoid space pia mater spinal cord filled with adipose tissue single layer brain no space blood vessels contains CSF blood vessels contains CSF attached to neural tissue attached to neural tissue double layer, outer layer fused to inner surface of cranial bones; contains veins called dural sinuses 2. cerebrospinal fluid (CSF) secreted into ventricles by ependymal cells at specialized structures called choroid plexuses fills ventricles and subarachnoid space around brain and spinal cord volume = 150 mL constantly produced BIOL 2404 Strong/Fall 2006 Chapter 8 Lecture Notes page 11 excess reabsorbed through arachnoid membrane into the superior sagittal sinus turnover is about three times a day main function is to float the brain 3. blood-brain barrier tight junctions between cells in brain capillaries blocks movement of many molecules between blood and brain tissue fluid loss of integrity can occur with prolonged stress or trauma H. nerve structure nerve = bundle of axons surrounded by layers of c.t. most nerves contain axons of both sensory and motor neurons cell bodies of sensory neurons are located in ganglia spinal nerves have dorsal root ganglia cranial nerves have ganglia in head cell bodies of motor neurons are located in gray matter all spinal nerves contain axons of motor neurons whose cells are in the lateral and ventral gray columns cranial nerves with significant motor content have axons originating from nuclei in the brain stem BIOL 2404 Strong/Fall 2006 Chapter 8 Lecture Notes page 12 I. cranial nerves (table 8-2) I olfactory - olfactory II optic - vision III oculomotor - motor control of intrinsic and extrinsic eye muscles IV trochlear - motor control of extrinsic eye muscles V trigeminal - see table VI abducens - motor control of extrinsic eye muscles VII facial - see table VIII vestibulocochlear - hearing and equilibrium IX glossopharyngeal - see table X vagus - autonomic motor control of organs of ventral body cavity including heart XI – accessory - see table XII - hypoglossal - see table J. spinal nerves and plexuses 31 pairs: organized by region of spinal cord spinal nerves are named for vertebrae: C1-C8*, T1-T12, L1-L5, S1-S5, Co1 some spinal nerves interconnect to form plexuses just outside the spinal column nerves leaving the plexuses contain axons from several spinal nerves cervical - neck and diaphragm (phrenic nerve) brachial - upper limb lumbar - lower limb sacral - lower limb (sciatic nerve) K. autonomic nervous system (ANS) 1. general pathway preganglionic neurons ganglia postganglionic neurons BIOL 2404 Strong/Fall 2006 Chapter 8 Lecture Notes page 13 2. organization a. dual innervation - both divisions innervate most of the same organs b. divisions have opposing effects 3. divisions a. sympathetic (“fight or flight”) - prepares the body for emergencies and exercise innervation is widespread control tends to be temporary (the sympathetic response) preganglionic neurons have their cell bodies in the thoracic and lumbar lateral gray horns they leave as part of spinal nerves and end in the sympathetic ganglia postganglionic neurons have their cell bodies in the ganglia and terminate in effector organs b. parasympathetic (“rest and digest”) - conserves energy innervation is localized duration of control may be brief (digestive organs) or long-lasting (heart) preganglionic neurons have their cell bodies in the brain stem and sacral lateral gray horns they leave as part of cranial (III, VII, IX, X ) or spinal nerves and end in the parasympathetic ganglia postganglionic neurons have their cell bodies in the ganglia and terminate in effector organs the vagus nerve (X) is the major parasympathetic innervator of organs in the ventral body cavity including the heart BIOL 2404 Strong/Fall 2006 Chapter 8 Lecture Notes page 14 4. neurotransmitters and receptors a. cholinergic neurons use ACh there are two main types of cholinergic receptors this allows ACh to cause different effects in different organs b. adrenergic neurons use norepinephrine (NE) there are several types of adrenergic receptors this allows NE to cause different effects in different organs preganglionic postganglionic sympathetic cholinergic adrenergic parasympathetic cholinergic cholinergic 5. the adrenal medulla is a modified sympathetic ganglion its neurons never developed axons they secrete epinephrine and norepinephrine directly into the blood during a sympathetic response this amplifies and prolongs the sympathetic response BIOL 2404 Strong/Fall 2006 Chapter 8 Lecture Notes page 15 6. specific effects on organs sympathetic parasympathetic pupils heart rate heart contraction force coronary and skeletal muscle blood vessels other blood vessels bronchioles digestive activity BIOL 2404 Strong/Fall 2006