Transcript Bioenergetics - Eastern Michigan University

The Nervous System
General Nervous System
Functions
• Control of the internal environment
– Nervous system works with endocrine system
• Voluntary control of movement
• Programming spinal cord reflexes
• Assimilation of experiences necessary for
memory and learning
Divisions of the Nervous System
Organization of the Nervous
System
• Central nervous system (CNS)
– Brain and spinal cord
• Peripheral nervous system (PNS)
– Neurons outside the CNS
– Sensory division
• Afferent fibers transmit impulses from receptors to CNS
– Motor division
• Efferent fibers transmit impulses from CNS to effector organs
Relationship between motor and sensory fibers of the
PNS and the CNS
Structure of a Neuron
• Cell body
• Dendrites
– Conduct impulses toward cell body
• Axon
– Carries electrical impulse away from cell body
– May be covered by Schwann cells
• Forms discontinuous myelin sheath along length of axon
• Synapse
– Contact points between axon of one neuron and
dendrite of another neuron
Parts of a neuron
Synaptic transmission
Resting Membrane Potential
• At rest all cells are negatively charged (including
neurons)
– Determined by concentration of ions (K+, Cl-, Na+)
• This negative charge is called Resting Membrane
Potential (~-40 to -70 mv)
• The RMP is maintained by the semi-permeable
cell membrane and intra vs extracellular
concentration gradient of ions
Sodium Potassium Pump
• The concentration gradient across the cellular
membrane is maintained by the Na+/K+ pump
• It uses ATP to actively pump Na+ out of the cell
and K+ into the cell
• It takes energy (ATP) to maintain the pump and
the gradient
Action potential
– Occurs when depolarization reaches threshold
• Permeability of the membrane changes, allowing
Na+ into the cell, making the interior positively
charged
– Repolarization
• Change in membrane permeability, restoring resting
membrane potential
Action potential is produced by an increase in sodium
conductance into the neuron
When a polarized nerve fiber is stimulated, sodium channels open,
some sodium ions diffuse inward and the membrane is depolarized
When potassium channels open, potassium ions
diffuse outward, and the membrane is repolarized
Neurotransmitters and Synaptic
Transmission
• Neurons communicate across synapses
using neurotransmitters
– Released from presynaptic membrane
– Binds to receptor on post synaptic membrane
• Excitatory transmitters
– Cause depolarization (EPSP)
• Inhibitory transmitter
– Cause hyperpolarization (IPSP)
Structure of a chemical synapse
Sensory Information
• Proprioceptors
– Provide CNS with information about body
position and joint angle
• Free nerve endings
• Golgi-type receptors
• Pacinian corpuscles
• Muscle chemoreceptors
– Provide CNS with information regarding the
metabolic rate of muscular activity
Reflexes
• Rapid, unconscious means of reacting to stimuli
• Order of events:
– Sensory nerve sends impulse to spinal column
– Interneurons within spinal cord activate motor neurons
– Motor neurons control movement of muscles
• Reciprocal inhibition
– EPSPs to muscles to withdraw from stimulus
– IPSPs to antagonistic muscles
The withdrawal reflex acts on the flexor muscle on
one side of the body and the extensor on the other
Somatic Motor Function
• Somatic motor neurons of PNS
– Responsible for carrying neural messages from
spinal cord to skeletal muscles
• Motor unit
– Motor neuron and all the muscle fibers it
innervates
• Innervation ratio
– Number of muscle fibers per motor neuron
A motor unit
Vestibular Apparatus and
Equilibrium
• Located in the inner ear
• Responsible for maintaining general
equilibrium and balance
• Sensitive to changes in linear and angular
acceleration
Vestibular apparatus in maintenance of equilibrium
and balance
Motor Control Functions of the
Brain
• Brain stem
• Cerebrum
– Cerebral cortex
• Organization of complex movement
• Storage of learned experiences
• Reception of sensory information
– Motor cortex
• Most concerned with voluntary movement
• Cerebellum
– Monitoring complex movement
Motor Functions of the Spinal
Cord
• Withdrawal reflex
• Contains groups of neurons capable of
controlling certain aspects of motor activity
• Spinal tuning
– Voluntary movement is translated into
appropriate muscle action
Structures and processes leading to voluntary
movement
Autonomic Nervous System
• Responsible for maintaining internal environment
– Effector organs not under voluntary control
• Smooth muscle, cardiac muscle, glands
• Sympathetic division
– Releases norepinephrine (NE)
– Excites an effector organ
• Parasympathetic division
– Releases acetylcholine (ACh)
– Inhibits effector organ
Neurotransmitters of the autonomic nervous system