Please enable JavaScript.
Coggle requires JavaScript to display documents.
Chapter 8-The Nervous System (8.2 Distinguish between neurons and…
Chapter 8-The Nervous System
8.1 The Nervous System has Anatomical and Functional Divisions
Nervous System
Monitors the internal and external environments
Integrates sensory information
Coordinates voluntary and involuntary responses of many other organ systems
Central Nervous Tissue
Brain and spinal cord
Integrates and coordinates the processing of sensory data and the transmission of motor commands
Sensory Input Function
PNS
Sensory Receptors (located at the neds of peripheral neurons): detect changes occurring in their surroundings
Once stimulated, sensory receptors transmit a sensory impulse to the CNS
Sensory Impulse: carried on a sensory neuron
Integrative Function
CNS
Involves interpretation of an incoming sensory impulse
i.e. decision is made concerning what's going to happen next, based on sensory impulse
Integration occurs in interneurons
A motor impulse begins
Motor Functions
PNS
Involves response of a body part
Motor Impulses are carried from CNS to responsive body parts called
effectors
Motor impulses carried on a motor neuron
Muscle Effector: contracts
1 more item...
Peripheral Nervous System
All neural tissue outside the CNS
Motor (Output From CNS) (Efferent Neurons
Autonomic (Effectors: Smooth muscle; Cardiac muscle; Glands) (Unconscious Control)
Sympathetic (Fight or Flight) (NT: Norepinephrine) (Adrenergic-Adrenaline)
Parasympathetic (Homeostasis) (NT: Acetylcholine)
Somatic (Effectors: Skeletal Muscle) (Conscious Control)
Sensory (Input into CNS) (Afferent Neurons)
Neuron: a specialized cell transmitting nerve impulses
8.2 Distinguish between neurons and neuroglia on the basis of structure and functions
Neuron: The structural & functional unit of the nervous system; a nerve cell
Neuron Structure
Cell Body: Central portion of neuron, contains usual organelles, except centroles
Neuron Processes/ Nerve Fibers
Dendrites: many per neuron, short and branched, receptive portion of a neuron, carry impulses toward cell body
Axons: one per neuron, long, thin process. carry impulses away from cell body
Axons in PNS
Large axons are surrounded by a myelin sheath produced by many layers of Schwann Cells (neuroglial cell)
Interruptions in the myelin sheath between Schwann cells-
Nodes of Ranvier
myelin- lipoprotein
Small axons do not have a myelin sheath
All axons in the PNS are associated with Schwann Cells
Axons in CNS
Myelin is produced by an
oligodendrocyte
rather than Scwann Cells
White Matter: A bundle of myelinated nerve fibers
PNS: Nerve
CNS: Tract/Column
Gray Matter: A bundle of cell bodies (or unmyelinated nerve fibers)
PNS: Ganglia/Ganglion
Nucleus
Regeneration of Nerve Fibers
Cell body injury= death of neuron
Damage to an axon may allow for regeneration
Neuroglial Cells= accessory cells of nervous system form supporting network for neurons; "nerve glue"
PNS: Schwann cells: Produces myelin
Satellite cells: nourish neurons
CNS= 4 types; provide bulk of brain and spinal cord tissue
Oligodendrocyte: looks like eyeball, Produces myelin
Astrocyte star-shaped, Nourishes neurons
Microglia: looks like spider, Phagocytosis
Ependymal cells: epithelial like layer, lines spaces in CNS (1. brain=ventricles. 2. spinal cord=central canal)
Classification of Neurons
Functional Classifications
Sensory Neuron: PNS, afferent neurons=carry sensory impulses from sensory to CNS, input information to CNS
Location of receptors
Somatic
External: touch, pressure, temp, sight, smell, hearing, &touch
Proprioceptors(position and movement)
Visceral receptors: digestive, respiratory, cardiovascular, urinary, reproductive, taste, deep pressure & pain
Interneurons (Association): CNS
link other neurons together (sensory to interneuron to motor neuron)
Motor Neurons: PNS, Efferent:carry motor impulses away from CNS and to effectors
output information from CNS
Effectors: muscles and glands
Somatic:Skeletal muslces. Visceral: Muscle and glands, Sympathetic: adrenergic, Parasympathetic: Cholingeric)
Structural Classifiction
Multipolar: Most common, many extensions, many dendrites lead toward cell body, one axon leads away from cell body
Bipolar: Rare, sight, smell, & hearing) two extension, one fused dendrite leads toward cell body, one axon leads away from cell body
Unipolar: Most PNS sensory neurons. One process from cell body, forms central and peripheral processes, only distal ends are dendrites
8.3 Describe the events involved in the generation and propagation of an action potential
Resting Nerve cells: resting neuron's cell membrane is polarized (electrically charged)
Potential Difference: difference in electrical charge between 2 points (i.e. across a cell membrane)
K+: High inside, Na+: High outside, Cl-: high outside
Resting Membrane Potential (RMP) of a nerve cell is -70mV or millivolts)
Membrane Potential
RMP can be disrupted in two ways
Hyperpolarization: more negative
depolarization: less negative
cell membrane of a neuron must be depolarized to -55mV in order to start a nerve impulse
Action Potential: When RMP is depolarized to -55mV
Threshold potential is -55mV, threshold stimulus is +15mV
After threshold is reached, rapid opening of Na+ channels result is rapid depolarization (reversal of the membrane potential to +30mV)
K+ channels open (while Na+ close)and repolarization occurs and recovery of the RMP to -70mV
Occurs in 1/1000 seconds
8.4 At synapses, communication occurs among neurons or between neurons and other cells
Nerve Impulse Transmission
Nerve Impulse (NI): the progregation of action potentials (AP) alnong a nerve fiber (length of neuron)
NI is an electrical impulse, impulse begins on a dendrite, runs toward the cell body, through the cell body, and down the axon
Characteristics of a NI
Refractory Period: period following a NI when a threshold stimulus cannot produce another NI
All or Nothing Response: if a nerve cell responds at all, it responds completely
Summation: many subthreshold stimuli received one after another may allow threshold potential to be reached, trigger an AP and begin a NI on a neuron
Conduction: The manner in which the NI runs down the nerve/neuron fiber
Unmyleinated nerve fibers: Ni must travel the length of the nerve fiber; slow
myelinated nerve fiber (Salutatory Conduction): NI jumps from Node of Ranvier to Node of Ranvier. Very fast
Synaptic (Chemical) Transmission
Synapse: junction between two neurons where a nerve impulse is transmitted
Occurs between the axon of one neuron and dendrite or cell body of a second neuron
The two neurons do not touch, There is a gap between them which is the synaptic cleft
Scheme of Synaptic Transmission
NI reaches axonal terminal of pre-synaptic neuron causing depolarization of synaptic knob
Ca+ channels open and calcium ions rush into axonal terminal
Causes synaptic vesicles (Filled with Neurotransmitter) to release NT via exocytosis (outside of cell) into the synaptic cleft
NT diffuses across synaptic cleft and depolarizes the post-synaptic neuron's membrane
An AP is triggered and a NI begins in the post-synaptic neuron
Neurotransmitters (NT)
At least 30 produced by CNS
Most common is Acetylcholine(ACh), released by all motor neurons and some CNS neurons
Monoamines (modified amino acids): widely distributed in the brain where they play a role in emotional behavior and circadian rhythm
Includes: Epinephrine, Norepinephrine, Dopamine, Serotonin, Histamine
Unmodified AA Include: Glutamate, aspartate, GABA (gamma aminobutyric acid, glycine
Fate of Neurotransmitter in Synaptic Cleft
Destruction of NT: Enzymes that are present in the synaptic cleft destroys NT
Reuptake of NT: Transported back into pre-synaptic knob
8.5 The brain and spinal cord are surrounded by three layers of membranes called the meninges
Meninges
The Dura Mater
Outermost layer, tough and fibrous, attached to the inner peritoneum of the skull, contains many blood vessels and nerves, DM splits into two layers where it encloses the dural sinuses (collects venous blood from brain).
Arachnoid
Middle layer, thin net-like membrane, beneath the arachnoid mater lies a wide space called sub-arachnoid space. Space is filled with cerebrospinal fluid and serves as a cushion for the brain
Pia Mater
Inner layer that clings to brain surface, very thin delicate CT, many nerves and blood vessels=nourishment, dips into grooves and contours
Spinal Cord
DM is not attached to bone of the vertebra, space between the DM and bone is called the epidural
Space between PM and AN is the subarachnoid
8.6 Discuss the roles of gray matter and white matter in the spinal cord
Gross structure of Spinal Cord
Length: 17 inches, start=foramen magnum, end=tapers to point (conus medullaris) and terminates near the intervertebral disc that separates 1st and 2nd lumbar vertebra
Contains 31 segments, cauda equina: the lower lumbar and sacral nerves travel downward
Cross-Sectional Anatomy
Gray Matter: butterfly, bundles of interneuron cell bodies, posterior dorsal horns, lateral horns, and anterior horns
located in central canal, gray commissure, anterior median fissure, posterior median sulcus
White Matter: myelinated (interneuron) axons
Loation: Posterior funiculi or white column, lateral funiculi, anterior funiculi
Ascending tracts: Located in posterior dorsal columns and conduct sensory (afferent) impulses from body parts
Descending tracts: located in anterior columns and conduct motor (efferent) impulses from the bran to effectors