Basal Humanbiologi Nervous System
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Nervous System
General Anatomy
CNS: brain, spinal cord. Efferent: somatic, transmits action potential to skeletal muscle; autonomic: sympathetic, prepare body for physical activity; parasympathetic, vegetative function, eg digest food.
PNS: cranial nerves(12) somatic connecting skin, skeletal muscle, autonomic connecting viscera; spinal nerves(31), ganglia, same as cranial nerves.
The Functions of the CNS
Medulla spinalis:
Corpus callosum: connect left and right cerebral hemispheres to each other.
Basale ganglia: muscle activity, posture, unintentional movement.
Diencephalon: thalamus (sensory relay center, mood, movement), hypothalamus (homeostasis, endocrine), epithalamus (olfactory stimulation – smell)
Mesencephalon: ascending, descending nerves. Visual reflex center, auditory pathway.
Pons: contain ascending, descending nerve tracts; relay between cerebrum, cerebellum; reflex.
Medulla oblongata: pathway for ascending descending nerve tracts; center for reflexes, eg heart beat, breathing, swallowing, vomiting.
Reticular formation: control cyclic activities, eg sleep-wake cycle.
Cerebullum: maintaining muscle tone, balance, coordination of movement.
Frontal lobe: voluntary movements and higher intellectual processes.
Parietal lobe: sensations involving temperature, touch, pressure, pain, and speech.
Occipital lobe: vision, visual images, and other sensory experiences.
Temporal lobe: hearing and smelling and for the interpretation of sensory experience and memory
Functions the PNS
Describe PNS. Functions of SNS (motor, sensory), ANS parted by cranial nerve, spinal nerve. Describe spinal nerve network in the nerve plexus. Name, function of cranial nerves, nerve ganglia that control arm, leg, diaphragma. Interpret knee-reflex.
Cranial Nerves
See Hole's Essential 8th edt, §9, p236, Figure 9.31
See Hole's Essential 8th edt, §9, p238, Table 9.6
Spinal nerves
Microscopic: rootlets combine form ventral root on anterior side, dorsal root on posterior. ventral root contains efferent (motor) fibers, dorsal root contains afferent (sensory) fibers. The dorsal and ventral roots join one another laterally form spinal nerve. Dorsal root contains a spinal ganglion, near where it joins the ventral root.
Macroscopic: 31 pairs of spinal nerves, exit the vertebral column through intervertebral foramen. 1st pair exits between the skull and 1st cervical vertebra. Nerves of sacrum exit through the sacral foramina. 8 exit through cervical region, 12 thoracic region, 5 lumbar region, 5 sacral region, 1 coccygeal region.
Plexuses: cervical: C1 – C4, motor impulses to muscle fibers of diaphragm, neck. Brachial C5 – T1. Lumboscaral: T12 – S5.
Reflex arc: 1. sensory receptor, dendrites sensitive to specific internal, external changes. 2. Afferent neuron, unipolar, transmits impulse from to spinal cord or brain 3. interneuron, conduct from sensory to motor neuron 4. motor neuron, transmits impulse to effect from SC or brain 5. effector organ, responds to stimuli.
Autonomic Nerve System of PNS
ANS is portion of PNS functions independently without conscious effort, transmits sensory information from visceral organs to the CNS and controls visceral functions by regulating the actions of smooth muscles, cardiac muscles, and glands, maintain homeostasis. 2 neurons between CNS and effector. Sympathetic, physical activity (adrenal gland), parasympathetic (static maintenance) divisions, antagonist of each other.
Parasympathetic Division preganglionic neuron cell bodies are in the brain stem and the lateral gray matter of the sacral part, and the postganglionic neuron cell bodies are within terminal ganglia. Parasympathetic fibers are cholinergic and secrete ACh at the ends of postganglionic fibers.
Sympathetic Division cell bodies of the postganglionic neurons are primarily within the sympathetic chain ganglia, except adrenal gland. Most sympathetic postganglionic fibers are adrenergic and secrete norepinephrine. A few are cholinergic, innervate sweat glands and some blood vessels in skeletal muscles.
Meninges, Ventricle System, Cerebrospinal Fluid Circulation
Meninges: protect the brain and spinal cord. Dura mater, arachnoid mater, and pia mater. Dura mater, composed of fibrous connective tissue, many blood vessels and nerves. Arachnoid mater, thin, weblike membrane, lacks blood vessels. Subarachnoid space, contains cerebrospinal fluid (CSF). Pia mater, very thin and contains many nerves, blood vessels, nourish underlying cells, hugs surfaces, follows irregular contours.
CSF: secreted by choroids plexuses, specialized capillaries at pia mater at walls of ventricles. May be reabsorbed into blood stream. Lumbar puncture, needle between 3 – 4 lumbar vertebrae, measure pressure or take biopsy.
Neuron, Excitation and Impulse conduction; Neurotransmitters
Beskrive opbygningen af neuron og myelinskede og mikroskopiske opbygning af en perifer nerve, perifert ganglion samt grå og hvid substans i CNS. Gør rede for hovedbegivenhederne ved excitation af og impulsledning i neuroner og impulsoverførsel imellem neuroner v.h.a. neurotransmittorer i synapser. Beskriv lokalisering og hovedvirkning af de vigtigste neurotransmittorer.
Microscopic, Neuron
Neuroglia:
Astrocyte: cover the surfaces of neurons and blood vessels, provide structural support, form the blood-brain barrier, thus regulating what substances from the blood reach the neurons.
Ciliated ependymal cells: lining the ventricles of the brain help to move cerebrospinal fluid. (CSF)
Ependymal cells on the surface of the choroid plexus secrete cerebrospinal fluid
Microglia: in CNS, phagocytize dead nervous tissue, microorganisms, foreign matter.
Oligodendrocyte: extensions form the myelin sheaths of axons within CNS.
Schwann cells: extension forms a myelin sheath, called neurilemma around each axon within the PNS.
Neuron: (dendrites, axon, Ranvier nodes, soma etc)
Sensory neurons: (afferent neurons) carry nerve impulses from peripheral body parts into the brain or spinal cord. either have specialized receptor ends at the tips of their dendrites, or they have dendrites that are closely associated with receptor cells in the skin or in sensory organs. Most are unipolar, some bipolar.
Interneurons: lie within brain or spinal cord, multipolar, link other neurons, transmit impulses from one part to another, direct incoming sensory impulses to appropriate parts for processing and interpreting.
Motor neurons: (efferent neurons) multipolar, carry nerve impulses out of the brain or spinal cord to effectors.
Excitation
Local potential: (sensory receptors) 1. stimulation of neuron environmental changes. 2. alters permeability of various ions leading to change in resting membrane potential. ↑ Na+ permeability - depolarization. ↑ K+ or Cl- permeability –hyperpolarization. (graded potential, decremental, reversible till stimuli ceases)
Action potential: (motor, transduction) Consists of rapid changes in membrane potential due to opening and closing of voltage-gated ion channels. begins with a steady depolarization - generator potential. If reaches threshold, the membrane continue to depolarize, follow repolarization then short period of hyperpolarization. (all-or-none, irreversible)
Threshold potential: ∆ resting membrane potential of a membrane is graded ≡ intensity of stimulation. If additional stimulation arrives before effect of previous stimulation subsides, phenomenon is summation - summated potentials, threshold potential may be reached.
Impulse transmission: synapse, presynaptic cell (neuron); postsynaptic- cell (neuron, muscle, gland)
1. nerve impulses arrive at synaptic knob, open ion gated Ca2+ canal. 2. triggers exocytosis, release neurotransmitter 3. vesicles in the reverse pool release NT, then move back to fill up, never leaves presynaptic cell. 4. NT bind to gate, Na+ enter, K+ exit. 5. Na+ depolarizes, postsynaptic potential.
... To be continued