The Nervous System Flashcards
2 structural subdivisions of the nervous system
- Central nervous system (brain & spinal cord)
2. Peripheral nervous system (cranial nerves, spinal nerves and ganglia)
Sensory Nervous system
- AKA
- what it does
- 2 components
-aka afferent nervous system
-Receives sensory info from receptors in PNS & transmits to CNS
2 components;
1. Somatic sensory
-general senses such as touch, pain, pressure, vibration & proprioception
-special senses such as taste, vision, balance, hearing and smell
2. Visceral sensory:
-impulses from viscera (generally temp & stretch)
Motor Nervous System
- AKA
- what it does
- 2 components
- AKA efferent nervous system
- sends impulses from CNS to muscles & glands
- 2 components;
1. Somatic motor (Voluntary)- impulses from CNS that cause contraction of skeletal muscles
- Autonomic motor (Involuntary)
- impulses from CNS that regulate smooth & cardiac muscles (as well as glands)
- impulses from CNS that cause contraction of skeletal muscles
2 cell types w/in nervous system
- Neurons (nerve cells)
- electrically excitable cells that initiate, transmit & receive nerve impulses
- approx. 35-100 billion neurons
- Glial cells (support cells)
- Nonexcitable cells that support and protect neurons -> provide an organized, supporting framework for all nervous tissue
- 100 billion - 1 trillion glial cells
- capable of mitosis (neurons can’t)
Neurons
-3 characteristics
-Basic structural unit of nervous system
-Conduct nerve impulses from one part of the body to another
CHARACTERISTICS;
-High metabolic rate (needs lots of O2, glucose)
-Extreme longevity (stay in body for whole life)
-Nonmitotic
Neuron structure
-3 main structural regions
- 3 main structural regions;
- Cell body
- Dendrites
- Axon
- Sends electrical impulses unidirectionally
Neuron; Cell body
- contains typical organs such as Nucleus, nucleolus, mitochondria, free ribosomes & rough ER.
- aka soma
- is control centre
- responsible for receiving, integrating & sending nerve impulses
Neuron; Dendrites
- Input
- short processes that branch from cell body
- Receive nerve impulses & carry them to cell body
- more dendrites = more impulses that can be received
- many also have dendrite spines to increase SA
Neuron; Axons
- what they do
- axon hillock
- synaptic knobs
- Myelin
- Output
- Transmit nerve impulses away from cell body & transmit info to other cells
- axon hillock = region where axon connects to the cell body
- neurons have 1 or no axons
- Synaptic knobs = end of axons that transmit impulse to effector cells
- Often covered in Myelin (insulating concentric layers that allow for faster nerve impulses)
Neuron Classification (Structurally; 3 types)
3 types depending on number of cell processes emanating directly from cell body;
- Unipolar: Single, short process that branches like a T (most sensory neurons of PNS)
- Bipolar: Two processes, one dendrite & one axon (relatively uncommon in humans -> primarily linked w/ special senses)
- Multipolar: many dendrites and a single axon (most common neuron e.g. motor neuron)
Neuron Classification (Functionally; 3 types)
-what they do
- Sensory (Afferent): transmit impulses from sensory receptors to CNS
- Motor (Efferent): transmit impulses from CNS to muscles or glands
- Interneurons: Facilitate communication between sensory and motor neurons
Glial Cells
- aka
- where found
- features
- aka neuroglia
- Found in both CNS & PNS
- Smaller than neurons & capable of mitosis
- Physically protect & nourish neurons
- more numerous than neurons
- Brain tumors more likely to be derived from glial cells than neurons
Glial Cells of the CNS (4 types)
- Astrocytes (most common)
- Ependymal cells
- Microglial cells
- Oligodendrocytes (same structure in PNS but have another name)
Glial Cell of CNS; Astrocytes
-Functions
-Most abundant FUNCTIONS -Helping form Blood-brain barrier (protects brain from toxins) -regulating tissue fluid composition -helping regulate synaptic transmission -forming structural network (aids in forming framework in brain) -replacing damage neurons -Assisting neuronal development
*hugs the capillary
Glial cells of CNS; Ependymal cells
-functions
- ciliated cuboidal epithelial cells that line ventricles of brain & central canal of spinal cord
- In conjunction w/ other glial cells, the ependymal cells produce cerebral spinal fluid (CSF) & form choroid plexus
Glial Cells of CNS; Microglial cells
-Function
- Small cells that are motile
- wander through the CNS & exhibit phagocytic activity, removing cellular debris from dead or dying cells
- aid in pathogen removal/detection
Glial cells of CNS; Oligodendrocytes
- where found
- what they do
- Associated w/ CNS axons only
- wrap themselves around axons like electrical tape
- produce myelin - is an insulator of electrical activity (allows faster electrical impulses along axon)
Glial Cells of PNS
- 2 types
- functions
2 types;
- Satellite cells: flattened cells arranged around neuronal cell bodies in ganglia
- Neurolemmocytes: aka Schwann cells - associated w/ PNS axons only
- wrap themselves around axons like electrical tape, produce myelin which is an insulator of electrical activity
- same structure & function as oligodendrocytes
Myelination of Axons
- Affects ability of neurons to conduct nerve impulses, also called action potentials
- Formed by neurolemmocytes in PNS and oligodendrocytes in CNS
- serves as insulation
Axon regeneration
- Damaged axons can regenerate if cell body is intact and critical amount of neurilemma remains
- depends on extent and site of damage
- neurolemmocytes play important role in process
Wallerian Degeneration
- Trauma severs axons
- Proximal portion of each severed axon seals off and swells - distal portion disintegrate
- neurileema and endoneurium form regeneration tube
- axon regenerates and remyelination occurs
- innervation to effector is restored
Nerves
-what they are
-3 layers
- Cablelike bundle of parallel axons
- Surrounded by three CT wrappings;
1. Endoneurium (within): around each individual axon
2. Perineurium (around): around individual fascicles
3. Epineurium (upon): around the entire nerve
*between fasicles = blood vessels
Synapses
- what they are
- 3 things a typical neuron consists of
-Specialized junctions b/w one axon and another neuron, muscle cell or gland cell Typical neuron; -Presynaptic neuron -Postsynaptic neuron -Synaptic cleft
*can be electrical or chemical
Autonomic Nervous system
-what it is
- is a complex system of nerves that govern involuntary actions
- works constantly w/ somatic nervous system to regulate body organs and maintain normal internal functions
- ANS and SNS both part of central nervous system & peripheral nervous system
- SNS operates under our conscious/voluntary control
- ANS operates under involuntary contraol - usu unaware of them
Comparison of Somatic & Autonomic Nervous system
- Both use sensory & motor neurons
- SNS: somatic motor neurons innverate skeletal muscle fibres, causing conscious voluntary movement
- Single lower motor neuron axon extends uninterrupted from spinal cord to one or more muscle fibers
- ANS motor neurons innervate smooth muscle fibers, cardiac muscle fibers or glands
- ANS motor neurons can either excite or inhibit cells in viscera
- two-neuron chain innervates muscles and glands
Two-neuron chain in ANS
- First neuron in ANS pathway is preganglionic neuron
- cell body in brain or spinal cord
- preganglionic axon extends to second cell body housed w/in autonomic ganglion in peripheral nervous system
- second neuron in pathway called ganglionic neuron
- a postganglionic axon extends from its cell body to effector cells
- two neuron chain vastly increases communication & control of ANS
ANS Subdivisions & what they do
- Sympathetic:
- mobilises body during extreme situations -> preparation of body for emergencies (fight or flight)
- Parasympathetic:
- maintenance activities and conserves body energy
- conservation of energy and replenishment of nutrient stores (rest and digest)
*two divisions counterbalance each other
Role of Sympathetic Division
- Fight or flight system
- E activities; Exercise, excitement, emergency & embarrassment
- promotes adjustment during exercise -> blood flow to organs is reduced
-e.g. HR increases, breathing rapid and deep, skin cold and sweaty and pupils dilate
Role of Parasympathetic Divison
- concerned w/ keeping body energy use low
- D activities; Digestion, defection and diuresis
- e.g. blood pressure, HR and respiratory rates low
- GI tract activity high
- skin is warm and pupils constricted
Autonomic nervous system
- Two systems of ANS service same visceral organs but work in opposition to each other (antagonistic)
- balanced to keep ourselves in a state of dynamic balance
