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Organization of the
NERVOUS System
3-28-12
Nervous System
• 3 Basic Functions:
• SENSORY Functions: detect stimuli both within and outside of the
body. Nerve cells which carry sensory information are called afferent
neurons
• INTEGRATIVE Functions: analyze info and determine the
appropriate response. Nerve cells which carry out this function are
called interneurons or association neurons
• MOTOR Functions: respond to output from interneurons. Nerve
cells which carry out this function are called efferent neurons
.
Nervous
System
Two main subsystems:
•
• CENTRAL NERVOUS SYSTEM (CNS)
• Brain & spinal cord
•
PERIPHERAL NERVOUS SYSTEM (PNS)
• All other nervous tissue that is further subdivided:
Somatic nervous system (SNS): motor neurons carry info from CNS to
skeletal muscles; axons are well myelinated and conduct impulses rapidly
Enteric nervous system (ENS): “brain of the gut”: control contraction of
smooth muscle in GI tract
Autonomic nervous system (ANS): motor neurons carry info from CNS to
smooth & cardiac muscle
Components of
AUTONOMIC NERVOUS SYSTEM:
– Chain of two motor neurons
Preganglionic neuron
Postganglionic neuron
– Conduction is slower due to thinly or
unmyelinated axons
MYELIN: an insulating lipid and protein covering produced by
Schwann cells in PNS and Oligodendrocytes (Greek for cells
with few branches) in CNS
GANGLION: group of nerve cell bodies located outside of the CNS
Tract: bundle of nerve cells inside the CNS
Two divisions of AUTONOMIC NERVOUS SYSTEM:
SYMPATHETIC and PARASYMPATHETIC
These two divisions typically work in opposition to one another
• Ex: the sympathetic nervous system would increase heart rate
in times of stress, and the parasympathetic nervous system
would decrease it
• SYMPATHETIC activities include body reactions in time
of physical or emotional stress
• fight-or-flight response
• Pupils dilate
• Heart rate increases
• Airways dilate
• Blood is routed away from non-essential organs
• Greater blood flow to skeletal muscle
• Non-essential processes are inhibited (digestion)
• PARASYMPATHETIC activities include normal body functioning
• “rest and digest” functions
• “SLUDD”:
• Salivation
• Lacrimation
(tear production)
• Urination
• Digestion
• Defecation
Anatomical Differences in Sympathetic
and Parasympathetic Divisions
Arise from different regions of the CNS
– Sympathetic –
also called the thoracolumbar
division
– Parasympathetic –
also called the craniosacral division
Anatomical Differences in Sympathetic
and Parasympathetic Divisions
Length of postganglionic fibers
– Sympathetic – long postganglionic fibers
– Parasympathetic – short postganglionic fibers
Branching of axons
– Sympathetic axons – highly branched
Influences many organs
– Parasympathetic axons – few branches
Localized effect
• Two cells types
Nervous Tissue
NEURONS: nerve cells
• Amitotic- do not divide
• Responsible for releasing
neurotransmitters and
conducting nerve impulses
Nervous
Tissue
three parts of a NEURON
• cell body: contains nucleus
surrounded by cytoplasm
with cellular organelles
• dendrites: receiving
portion of the neuron.
Short and highly branched,
arising from the cell body
• axon: conducts nerve
impulses towards another
neuron, muscle cell or gland
cell. Long and thin
Nervous Tissue
• Neuroglia: 2nd nervous system cell type
• support and protect neurons
• Much smaller than neurons, but 5-50 times more
numerous
• Able to divide
Neuron Function – Nerve Impulses
Some new, some review physiology information in WINGERD
questions
(#’s 48 – 72)
Pages 245 – 251 Wingerd text
Pages 222 – 227 your Tortora Text
Spinal Reflexes
SPINAL REFLEXES
fast, automatic responses to sensory impulses
– Autonomic reflexes: involving smooth muscle, cardiac muscle, glands
ex: swallowing
– Somatic reflexes: (somatic means body)
involve skeletal muscles
ex: patellar reflex (knee jerk)
Spinal Reflexes
The pathway followed by nerve impulses
producing reflexes is called the REFLEX ARC:
COMPONENTS OF REFLEX ARC:
– Receptor: the distal end of the sensory neuron that responds to a stimulus and
generates nerve impulse(s)
– Sensory (afferent) neuron: conduct impulse from sensory receptor to the axon
terminals
– Integrating center: within the spinal cord: synapse between sensory & motor neuron;
interneuron/association neuron
– Motor (efferent) neuron: carries impulse triggered by integrating center out of the
spinal cord and to body
– Effector: part of the body responding to the motor nerve impulse; action of the
effector is called the reflex