Formation of the Central Nervous System (CNS)?
- Neural tube forms and sinks below surface
- a. forward end forms brain
- b. back end forms spinal cord
- fluid filled cavity becomes central canal and ventricles
- Cerebral Spinal Fluid (CSF)
- study of nervous system
- is a control system: communicates with and controls other sytems
Brain and Spinal Cord
Peripheral Nervous System (PNS)
- Sensory (afferent carry toward) Division
- a. nerve fibers (axons) that convey impulses to the CNS from sensory receptors
- Motor (efferent carry away) Division
- a. transmits impulses from the CNS to effector organs
- b. two subdivisions
Motor division of PNS subdivisions:
- Somatic Nervous System
- a. skeletal muscle
- b. "voluntary nervous system"
- c. somatic motor nerve fibers
- Autonomic Nervous System (ANS)
- a. regulate the activity of smooth and cardiac muscle and glands
- b. "involuntary nervous system"
- c. visceral motor nerve fibers
Functional subdivisions of the ANS?
- Sympathetic Nervous System
- a. "Fight or Flight"
- Parasympathetic Nervous System
- b. slows down body
Cells of the Nervous system:
- Neurons: functional and structural units of NS
- Neuroglia: accessory support and protective cells for neurons, function much like c.t. in other parts of body
Neuroglia in PNS
Schwann cells- provide insulation on axon
Neuroglia in CNS
- Astrocyte: interface nerve tissue and blood vessel
- Oligodendrocyte: provide myelin sheath
- Microglia: active and increase in number during inflammation of CNS
- Ependyma: form an epithelial like membrane that is one cell thick and covers inside spaces within brain (ventricles, central canal), important in the blood-brain barrier: choroid plexus= capillary network associated with ventricles
Neurons: cannot divide but may generate new branch. Three Basic parts:
- Cell Body:
- a. makes neurofibrils for transporting material around neuron.
- b. centrosome (mitotic apparatus) missing
- a. short, numerous, highly branched fibers from cell body
- b. carry impulses to cell body
- a. usually one, long, larger, uniform in diameter process from cell body
- b. carry impulse away from cell body
- c. hillock-where leaves cell
- d. collateral-branches of axon
- e. ends specialized for synapse with another cell (presynaptic terminal)
Functional Classification of Neron:
- Sensory (afferent): to CNS
- Motor (efferent): away from CNS; to effector (muscle or gland)
- Association (interneuron): totally in CNS, between sensory and motor neurons, 90% are in this catergory
Structural Classification of Neuron:
- Unipolar: one process from cell body
- ex. in ganglia of spinal nerves
- Bipolar: two processes from cell body. 1 axon 1 dendrite
- ex. special sensory- eyes, nose, ears
- Multipolar: one axon and may dendrites
- ex. in brain most are this type
Gap in an axon myelinated sheath?
Node of Ranvier
Dense collection of myelinated fibers and axon.
Mostly nerve cell bodies and dendrites
- a. collection of neuron fiber inside CNS
- b. collection of neuron fiber outside CNS
c.t around one neuron
c.t. around bundle of neurons
c.t. around all fibers; contains blood vessels, fat
- a. Sensory
- b. Motor
- c. Mixed
nerves originating from spinal cord that communicate with other body parts
originating from the brain that communicate with other body parts
collection of neuron cell bodies outside the CNS
collection of neuron cell bodies inside the CNS
- a junction between two cells
- ex. nerve-nerve, nerve-muscle, nerve-gland
before the gap
after the gap
gap between cells
Types of Synapse?
- Electrical: proteins actually embedded in both cell membranes, provide channels for ion flow.
- Chemical: most fit in this category, axon with synaptic bulb that contain vesicle with neurotransmitters
time required to actually cross cleft (about .5 msec)
depletion of neurotransmitters in vesicles, cannot synthesize fast enough
- competes for Ach receptor sites
- inhibits contraction
Diisopropyl fluorophosphate / neostigmine / physostigmine?
combine with acetylcholinesterase and deactivates it: this allows continued contraction and leads to spasm
inhibits Ach release
Caffeine / benzedrine / nicotine?
reduce threshold for excitation and therefore result in facilitation