Transcript Nervous System

Anatomical Organization of
the Nervous System
• Central nervous system (CNS)
– consists of the brain located
within the skull and the spinal
cord located within the vertebral
foramen
– integration and command center
of the body
• Peripheral nervous system (PNS)
– consists of nerves (extensions of
the CNS) that connect the CNS to
all other locations in the body
Nervous System
• One of 2 controlling and communicating systems of
the body (other is the endocrine system)
• Transmit sensory information
– propagate APs to the CNS following a stimulus
which has changed a variable from its set point
• from eyes, skin, blood vessels, ears, digestive
tract, joints, muscles, lungs…
• Integration
– interpretation of sensory information by the CNS
• type, location and magnitude of stimulus
• Transmit motor information
– propagate APs from the CNS to various effector
organs throughout the body
• provides a way to respond to stimuli
Cells of the Nervous System
• The two principal cell types of the nervous system are:
– Neurons
• hundreds of thousands of neurons extend axons
and make synapses all over the body with other
neurons, muscles and glands
• communicate through action potentials
• allows for short response times to changes in
homeostasis
– Neuroglia
• guide developing neurons to make synapses
• provide a supportive scaffolding for developed
neurons
Neuron Types of the Nervous System
• Sensory (afferent)
– associated with sensory receptors
– propagate APs via the PNS toward the CNS
• Interneurons
– integrate information within the CNS
– receive APs from sensory neurons and initiate APs
in motor neurons
• Motor (efferent)
– propagate APs via the PNS away from the CNS
• All 3 neuron types are used to respond to stimuli
– reflex
Basic Function of the Nervous System
Functional Organization of the Nervous System
Myelination of Neurons of the Nervous System
• Some neurons in the CNS are myelinated, while most
are unmyelinated
• All of the neurons in the PNS are myelinated
• Areas of the CNS that are made of myelinated
neurons are called white matter
– represent the locations of long sensory and motor
neurons
• Areas of the CNS that are made of unmyelinated
neurons are called gray matter
– represent the locations of short interneurons which
make many synapses for integration to process
sensory information and initiate motor information
Spinal Cord
• The spinal cord is attached to the brain and extends to
the lumbar region of the vertebral column
• Functions include:
– integration of basic stimuli presented to the body
below the neck through simple reflexes
• withdrawal reflex in response to pain
– sending sensory and motor information to and from
the brain
Spinal Cord Anatomy
• Dorsal (posterior) horns (left and right)
– sensory information enter the cord on the dorsal
aspect where they synapse with interneurons or
motor neurons
– extend into dorsal roots and ganglia (group of cell
bodies outside the CNS)
• Ventral (anterior) horns (left and right)
– motor information exits the cord on the ventral
aspect where they control effectors (muscle or
glands)
– extend into motor roots
• Dorsal and ventral roots merge together to form spinal
nerves
Spinal Cord Anatomy
Brain
Cerebral Cortex
• 4 lobes
– frontal, parietal, temporal and occipital
– location of interneurons for perception of all senses
– site of memory, emotion, learning
– site of initiation of voluntary skeletal muscle
contraction
The Cerebellum
• Protrudes under the occipital lobes of the cerebrum
• Makes up 11% of the brain’s mass
• Modifies the motor information leaving the motor
cortex
– provides precise timing and appropriate patterns of
skeletal muscle contraction to maintain balance and
coordination
• Cerebellar activity occurs subconsciously
Brain Stem
• Comprised of the pons and the medulla oblongata
• Clusters of neurons (brain centers) in regions of the
pons and medulla control the basic life functions:
– heart rate
• controlled by the cardioacceleratory and
cardioinhibitory centers in the medulla
– blood pressure
• controlled by the cardioacceleratory,
cardioinhibitory, and vasomotor centers in the
medulla
– breathing rate
• controlled by the inspiratory and expiratory
centers in the medulla and pons, respectively
• Control of effectors occurs through the Autonomic
Nervous System
Peripheral Nervous System
• The PNS consists of nerves (bundles of axons)
– propagate APs to and away from the CNS
– 12 pairs (left and right) of cranial are connected to
the brain and 31 pairs (left and right) of nerves are
connected to the spinal cord
• Sensory (afferent)
– all axons carry impulses from sensory receptors via
the PNS to the CNS
• Motor (efferent)
– all axons carry impulses via the PNS from CNS
• Mixed
– a mixture of sensory and motor neurons that carry
impulses via the PNS to and from CNS
– most common type of nerve in the body
Nerves
• Nerve
– cordlike organ of the PNS consisting of axons
enclosed by connective tissue
• Connective tissue coverings include:
– Endoneurium
• loose connective tissue that surrounds each
individual axon
– Perineurium
• coarse connective tissue that bundles axons into
fascicles
– Epineurium
• tough fibrous connective tissue around a nerve
Structure of a Nerve
Reflexes
• A rapid, predictable motor response to a stimulus
• Reflexes can be:
– simple
• involve peripheral nerves and the spinal cord
–rapid
– learned (acquired)
• involve peripheral nerves and require thought
–slower
• Following a stimulus, the sensory and motor
information of a reflex follows a pathway called a
reflex arc
– in many spinal reflexes, the effector is nearby the
location of the stimulus
Reflex Arc
• There are five components of a reflex arc
– Receptor
• detect stimulus
– Sensory neuron
• transmits the afferent impulse to the CNS
– Integration (control) center
• region within the CNS where synapses
(processing of sensory info) occur
– Motor neuron
• sends efferent information to an effector
– Effector
• muscle fiber or gland that responds to the
efferent impulse
• the activity of the effector depends upon the
magnitude of the stimulus
Sensory Receptors
• Structures specialized to respond to stimuli:
– nerve endings (dendrites of neurons)
– sense organs
• nerve endings combined with other tissue types
to enhance detection of a stimuli
–example: taste buds
• Mechanoreceptors
– respond to touch, pressure, stretch and itch
• Thermoreceptors
– respond to changes in temperature
• Photoreceptors
– respond to light
• Chemoreceptors
– respond to chemicals
• Nociceptors
– respond to pain
Neural Integration of the CNS
• Qualitative information (salty, pain or temperature)
depends upon which neurons are propagating APs
• Quantitative (strength) information depend on:
– the number of neurons that are firing APs
– the frequency of APs fired per neuron
Sensory Division of the Peripheral NS
Sensory division
• made of afferent neurons
– somatic
• sensory neurons send APs from skin, skeletal
muscles, and joints
– visceral
• sensory neurons send APs from organs within
the abdominal and thoracic cavaties
Motor Division of the Peripheral NS
Motor division
• made of efferent neurons control the action of
effectors
– somatic
• motor neurons send APs to voluntary skeletal
muscle
– visceral
• motor neurons send APs to involuntary cardiac
muscle, smooth muscle and glands
–a.k.a. the Autonomic Nervous System (ANS)
–2 antagonistic (opposing) divisions
• Sympathetic
• Parasympathetic
–the two divisions control the same effectors
(with few exceptions) but create opposite
responses in the effectors
Motor Pathways of the Somatic Nervous Division
vs. Autonomic Nervous Division
Autonomic Nervous System
• Visceral motor neurons of the Peripheral NS control
the activity of involuntary effectors such as cardiac
muscle, smooth muscle and glandular secretion
affecting:
– heart rate
– breathing rate
– sweating
– digestion
– blood pressure
• Action potentials in these motor neurons are initiated
in the medulla oblongata and the pons
– these motor neurons exit the brain by:
• descending tracts of the spinal cord
–exit spinal cord via spinal nerves
• cranial nerves
Function of the Sympathetic Division
• The sympathetic division is called the “fight or flight”
system
– activated when the body needs to expend energy
• Involves E activities
• exercise, excitement, emergency, and embarrassment
• Promotes necessary changes during these activities
– increases heart rate, blood pressure, respiration
rate, blood flow to skeletal muscles, glucose
metabolism
– decreases the activity of and blood flow to the
digestive system organs
• Its activity is illustrated by a person who is threatened
Function of the Parasympathetic Division
• The parasympathetic nervous system is called the
“rest and digest” system
– activated when the body needs to conserve energy
• Involves the D activities
– digestion, defecation, and diuresis (urination)
• Promotes necessary changes during these activities
– decreases heart rate, blood pressure, respiration
rate, blood flow to skeletal muscles, glucose
metabolism
– increases the activity of and blood flow to the
digestive system organs
• Its activity is illustrated in a person who relaxes after
eating a meal
Efferent Pathways of the ANS
• Efferent pathways of the ANS consist of a two-neuron
chain between the brain or spinal cord and the effector
– synapses between the neurons occur at ganglions
– The cell body and dendrites of the preganglionic
neuron is located in the CNS and the axon extends
along a nerve to the ganglion
– The cell body and dendrites of the postganglionic
neuron is located in the ganglion and the axon
extends to an effector organ
Organization of
the Sympathetic
Division
Organization of the
Parasympathetic
Division
Motor Pathways of the Somatic Nervous Division
vs. Autonomic Nervous Division
• All somatic motor neurons exocytose ACh
– ACh binds to nicotinic acetylcholine receptors on
the skeletal muscle fiber leading to its contraction
• All preganglionic motor neurons exocytose ACh
– ACh binds to nicotinic acetylcholine receptors on
the postganglionic neuron creating an AP
• All parasympathetic postganglionic motor neurons
exocytose ACh
– ACh binds to muscarinic acetylcholine receptors on
the effector tissue/organ causing a response
• All sympathetic postganglionic motor neurons
exocytose norepinephrine NE
– NE binds to adrenergic receptors on the effector
tissue/organ causing a response
Efferent Sympathetic vs. Parasympathetic
Effects of Neurotransmitters of the ANS
• The way the 2 divisions of the ANS can create
opposite responses in the effectors that they control is
by the release of different neurotransmitters onto the
cells of the effectors
• The cells of each organ controlled by the ANS have
membrane receptors to BOTH ACh and NE
– organs are dually controlled
• The response of the organ is determined by the
identity of the neurotransmitter released
– the binding of ACh to its receptor will cause the
effector to respond in one way
– the binding of NE to its receptor will cause the
effector to respond in the opposite way
• The effect of ACh and NE is effector specific
– NE increases heart rate, ACh decreases heart rate
– NE decreases the secretion of saliva, ACh
increases the secretion of saliva
Dual Control by the
Sympathetic and
Parasympathetic
Systems