The Nervous System
Terms
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- 3 functions of nervous system
- 1. Collects sensory input from the environments both inside and outside the body called stimuli 2. Processes the input and makes decisions as to the reaction called integration 3. Effects a response called motor output
- 2 major nervous systems
- 1. Central Nervous System (CNS) - consists of brain and spinal cord 2. Peripheral Nervous System (PNS) - Consists of nerves that extend from the brain and spinal cord (plexus)
- Afferent Nerves
- Sensory; nerve fibers send impulses to the central nervous system
- Efferent Nerves
- Motor; nerve fibers carry impulses away from the central nervous system
- Somatic Nervous System
- Voluntary; skeletal muscles
- Autonomic Nervous System
- Involuntary; cardiac muscle, smooth muscle and "stretch relex" in skeletal muscle
- Sympathetic
- "Fight-or-Flight"
- Parasympathetic
- "Rest and Digest" digestive system activated
- Soma
- Houses cell parts. Nucleus, mitochondria, Golgi bodies, endoplasmic reticulum
- Dendrite
- Receive signals and travel to
- Axon
- Carries impulses away. Mulitple collaterals branch off of axon called axonal terminals
- Schwann Cells
- Grow around the axon and produce the myelin sheath in the PNS
- Myelin Sheath
- White, fatty, waxy material called myelin which covers the axon and increases the rate or transmission
- Nodes of Ranvier
- Tiny gaps of the myelin sheath
- Axon Terminals
- Multiple collaterals branch off of axon
- Synapse
- The end of axon and transfers impulses from neuron to neuron
- Synaptic Cleft
- Gap between synaptic terminal and target tissue (20 nm in length)
- Astrocytes
- Anchor neurons to blood supply
- Microglia
- Phagocytes that dispose of debris
- Ependymal Cells
- Cilia that circulate cerebrospinal fluid
- Oligodendrocytes
- Create Myelin Sheath in CNS
- White Matter
- Contains myelin sheath (Protected)
- Gray Matter
- Unmyelinated fibers (unprotected)
- Afferent
- Sensory; Location of the soma, dendrites, and axon Ganglion - Axon travels to the CNS
- Efferent
- Motor; Soma is in the CNS but the axon leaves and becomes peripheral
- Interneuron
- Association; Relayers; found in the CNS
- Ganglion
- Small collection of cell bodies found outside the CNS
- 4 types of sensory receptors
- Naked Nerve Endings, Meissner Corpuscles, Pacinian Corpuscles, Proprioceptors
- 3 types of neurons
- Afferent, Efferent, Interneuron
- Naked Nerve Endings
- Feel pain and temperature
- Meissner Corpuscles
- Feel touch
- Pacinian Corpuscles
- deep pressure
- Proprioceptors
- muscle spindle; located in muscle or tendon concerned with locomotion and posture
- 3 shapes of neurons
- Multipolar, Unipolar, Bipolar
- Multipolar
- One soma, one axon, multiple dendrites interneurons and motor neurons
- Unipolar
- runs to spinal cord, second branch runs to body and receptors soma found in ganglion single branch running to cell body, sensory
- Bi Polar
- ears "receptors for special senses" dendrite with soma in between found in eyes, nose cell has one axon and one body
- Reflex
- Rapid, Predictable, and Involuntary responses to stimuli
- Reflex Arc
- Neural pathways that reflex travel down
- 5 items found in all reflex arcs
- sensory receptor, afferent neuron, integration center - CNS, efferent neuron, effector organ
- 2 types of reflexes
- Somatic and Autonomic
- Somatic Reflexes
- All the reflexes that stimulate skeletal muscles
- Autonomic Reflexes
- Reflexes that don't involve skeletal muscle glands
- Two Neuron Reflex Arc
- Monosynaptic, knee-jerk relex and babinski sign (no interneuron). Two neuron
- Three Neuron Reflex Arc
- Polysnaptic, withdrawl reflex (flexor) cause affected muscle to flex
- Cross Fiber Reflex Arc
- Reflex arc stimulates flexors and inhibits extensors on side of injury while simultaneously stimulates extensors and inhibits flexors on colateral (opposite side) of body
- Size of Spinal Cord - Cauda Equina - Number of Spinal Nerves
- 31 segments (between each vertebrae a nerve arises) 17 inches long (42 cm) Ends at the last thoracic vertebrae (T12) at last rib
- 3 layers of meninges
- Duramater, Arachnoid Mater, Pia Mater
- Duramater
- Outermost, tough and leathery, double layer membrane around skull, one layer is attached to skull, single layer
- Arachnoid Mater
- Middle, weblike 2nd layer
- Subarachnoid Space
- Filled with cerebrospinal fluid (located between arachnoid mater and pia mater)
- Pia Mater
- Innermost, extremely delicate layer
- Cerebrospinal Fluid
- Circulates around brain and spinal cord, nourishes brain and removes waste Similar to blood plasma - extremely watery Contains less proteins and more vitamin C Drains openings in 4th ventricle travel around outside of brain
- Pathway of Cerebrospinal Fluid
- 1. Choroid Plexus - capillaries located in roof of the ventricles that make CFS Lateral Ventricles - 3rd Ventricle - Through Cerebral Aqueduct - 4th Ventricle - Can exit and circle brain or enter central canal of spinal cord - absorbed into bloodstream at arachnoid villi
- Blood Brain Barrier
- The brain is surrounded by the latest permeable capillaries (water soluable) only water, glucose and essential amino acids can pass through fat soluable molecules can enter easily. ex. alcohol, nicotine, anethete, toxins, urea, proteins and most drugs are prevented from entering the brain tissues
- Axon
- Part of Single Neuron
- Endoneurium
- Protective covering of a single axon
- Fascicle
- Group of axons, together
- Perineurium
- Protective covering of a fascicle
- Nerve
- Group of fascicles together
- Epineurium
- Protective covering of the entire nerve
- How Many Spinal Nerves Are There?
- 32 pairs - that attach directly to the spinal cord and exit between each segment of vertebrae
- Rami
- Spinal Nerve splits into branches which move dorsally and ventrally
- Dorsal Rami
- Never form plexuses - back, motor and sensory
- Ventral Rami
- Plexuses - cervical, lumbar, sacral, bracial
- 4 Plexuses
- Cervical, Lumbar, Sacral, Bracial
- Cervical
- Phrenic Nerve - serves muscle of shoulder and neck diaphragm Injury to phrenic nerve leads to respiratory paralysis
- Brachial
- Muscultaneous - Bicep Axillary - Deltoid Radial - Triceps Wrist Flexor Median - Wrist Flexor, Hand Ulnar Nerve - Wrist Flexor - Hand
- Lumbar
- Femoral - Lower abdomen, Rectus Femoris Obturator - Hip Adductor Muscles
- Sacral
- Sciatic - largest nerve fibular and tibular Lower Leg Muscles
- Somatic Motor Pathway
- Contains no ganglions outside the central nervous system axon reaches all the way to effector
- Autonomic Motor Pathway
- Contains 2 neurons outside the CNS and one ganglion (group of cell bodies) outside the CNS
- Preganglionic Neuron
- Axons leave the CNS (either the brain or spinal cord) and synapses at the ganglion (long)
- Postganglionic Neuron
- Extends from the ganglion to the visceral organ (short)
- Preganglionic - Parasympathetic
- Cranial Nerves, and Sacral Spinal Nerves
- Terminal Ganglion - Parasympathetic
- Effector Organ
- Preganglionic - Sympathetic
- Spine between the T1 - L2 vertebrae and are connected together fro a unified response
- Sympathetic Chain
- Trunk; Located outside the CNS on the ventral ramus and connect vertically with the ganglion above it
- Eyes - Parasympathetic
- Constrict Pupil
- Eyes - Sympathetic
- Dilates Pupils
- Salivary Glands - Parasympathetic
- Activates Salivary Digestive System
- Salivary Glands - Sympathetic
- Inhibits Digestive Salivary (dry mouth)
- Heart - Parasympathetic
- Slows down
- Heart - Sympathetic
- Increase speed
- Lungs - Parasympathetic
- Constricts bronchioles
- Lungs - Sympathetic
- Dilates bronchioles
- Stomach - Parasympathetic
- Activate the stomach
- Stomach - Sympathetic
- Constrict the spencters
- Pancreas - Parasympathetic
- Activates pancreas
- Pancreas - Sympathetic
- Shuts down pancreas
- Liver - Parasympathetic
- No effect
- Liver - Sympathetic
- Break down glycogen to produce glycogen
- Adrenal Glands - Parasympathetic
- No effect
- Adrenal Glands - Sympathetic
- Produces epinephrine, and nonepinephrine
- Conductivitity
- Motor; The ability to transfer impulses to other neurons, muscles, or glands
- Irritability
- Sensory; The ability to respond to a stimulus and results in a nerve impulse
- Threshold Stimulus
- Weakest Stimulus capable of producing a response. (Minimum Amount)
- Nerve Impulse
- Quick depolarization followed by a quick repolarization travels at full strenght and length through axon
- Depolarization
- When the neuron is stimulated then "sodium gates" open, allowing sodium ions to rush into the cell via diffusion. This rush equals the ion charge
- Repolarization
- Potassium gates open allowing the potassium ions to rush out reestablishing the polarization - a neuron cannot conduct another impulse until it is polarized
- Concussion
- Slight injury resulting in dizziness
- Contusion
- Tissue damage occurs - if the brain stem then coma can occur - if to cerebral areas you can remain conscious
- Cerebral Edema
- Swelling on the brain due to injury compresses vital brain tissue
- Inter cranial Hemorrhage
- Bleeding from a ruptured blood vessel - compresses vital neurons
- Stroke
- Cerebrovascular Accident; 3rd leading cause of death - blood circulation is lost
- Hydrocephalus
- Accumulation of CSF in the brain
- Meningitis
- Inflammation of the meninges can be serious if bacteria or virus spreads to the brain
- Multiple Sclerosis
- Myelin Sheath is slowly destroyed, sheaths become hardened, person loses control of muscles
- Broca's Aphasia
- Not able to say what you want to say damage to the brocas area
- Parkinson's Disease
- Lose dopamine and muscles being shaking doamine shuts down muscles
- Epilepsy
- To many neurons firing at once cause a breakdown of the nervous system
- Alzheimers
- Brain cells dying rapidly and brain is loosing brain mass
- Encephalitis
- Inflammation of the brain
- Sclerosis
- Sheaths become hardened