CNS- Structure and Function W3 Flashcards
What are the functions of the nervous system?
Control of the internal environment
Voluntary control of movement
Spinal cord reflexes
Assimilation of experiences necessary for memory and learning
What does control of the internal environment involve?
Perceiving and responding to events in the interval/external environment
Where is the CNS?
Brain and spinal cord
Where is the PNS?
Neurons outside the CNS
What is the sensory division?
Afferent fibres which transmit impulses from receptors to CNS
What is the motor division?
Efferent fibres transmit impulses from CNS to effector organs
What is the somatic sensory?
Sensor input that is consciously perceived from receptors (eyes, ears and skin)
What is the visceral sensory?
Sensory input that is not consciously perceived from receptors of blood vessels and internal organs (heart)
What is the somatic motor?
Motor output that is consciously or voluntarily controlled; effector is skeletal muscle
What is the autonomic motor?
Motor output that is not consciously or is involuntarily controlled
Effectors are cardiac muscle, smooth muscle and glands
What part of the nervous system is input?
Sensory Nervous System
Somatic Sensory
Visceral Sensory
What part of the nervous system is output?
Motor Nervous System
Somatic Motor
Autonomic Motor
What is the sensory nervous system?
Detects stimuli and transmits information from receptors to the CNS
What is the motor nervous system?
Initiates and transmits information from the CNS to effectors
What is an axon?
Carries electrical message (action potentials) away from cell body
Covered by Schwann cells
What are Schwann cells?
Form discontinuous myelin sheath along length of axon
What is a synapse?
Contact points between axon of one neuron and dendrite of another neuron
What causes a greater speed of neural transmission?
Increase in the diameter of an axon
Increase in myelin sheath
What type of tissue are neurons?
Excitable tissue
What is magnitude of rest potential determined by?
Permeability of plasma membrane to ions
Difference in ion concentrations across membranes (Na+, K+, Cl- and Ca+2)
What is the negative charge of a cell at rest (polarised)?
-5 to -100mv
-40 to -75mv in neurons
How is the exchange of sodium and potassium across cell membranes maintained?
Maintained by sodium-potassium pump
What does the Na+/K+ pump do during the exchange of sodium and potassium across cell membrane?
Moves 2 K+ in and 3 Na+ out
Potassium tends to diffuse out of the cell
What is the all-or-none law for action potentials?
Once a nerve impulse is initiated, it will travel the length of the neuron
What is repolarisation in action potentials?
Returns to resting membrane potential
- K+ leaves the cell rapidly
- Na+ channels close
What is an action potential?
Occurs when a stimulus of a sufficient strength depolarises the cell
What does an action potential do?
Opens Na+ channels, and Na+ diffuses into the cell
Causes the inside of the cell to become more positive
What is a neurotransmitter?
Chemical messenger from presynaptic membrane
What does a neurotransmitter bind too?
A receptor on postsynaptic memrbane
What does a neurotransmitter cause?
Depolarization of postsynaptic membrane
What are the 2 types of neurotransmitter?
Excitatory (EPSP)
Inhibitory (IPSP)
How can EPSPs promote neural depolarization?
1) Temporal summation
2) Spatial summation
What is temporal summation (EPSP)?
Rapid, repetitive excitation from a single excitatory presynaptic neuron
What is spatial summation (EPSP)?
Summing EPSPs from several different presynaptic neurons
What does EPSP stand for?
Excitatory postsynaptic potential
What does IPSP stand for?
Inhibitory postsynaptic potential
What does IPSP cause?
Hyperpolarization
What is hyperpolarization?
More negative resting membrane potential
By having neurons with a more negative membrane potential, what does this cause?
Resistance to depolarization
What happens when neurons moves towards the threshold?
EPSP> IPSP
What are muscle proprioceptors (mechanoreceptors)?
Muscle spindles
Golgi Tendon organs
What are joint proprioceptors?
Free nerve endings
Golgi type receptors
Pacinian corpuscles
What are free nerve endings?
Most abundant
Touch, pressure
What are Golgi type receptors?
Found in joint ligaments
What are Pacinian corpuscles?
Tissues around joints/skin
What is proprioception?
Sense of the body’s position in space based on specialised receptors that reside in the muscles, tendons and joint
What are proprioceptors?
Sensors that provide information about joint angle, muscle length and muscle tension, which is integrated to give information about the position of the limb in space
What are muscle spindles?
Responds to changes in muscle length
What do muscle spindles consist off?
Intrafusal fibres
Gamma motor neurons
What are intrafusal fibres?
Run parallel to normal muscle fibres (extrafusal fibres)
What are gamma motor neurons?
Stimulate intrafusal fibres to contact with extrafusal fibres (by alpha motor neuron)
What is a stretch reflex?
Stretch on muscle causes reflex contraction
How does a muscle spindle work?
1) Detect stretch of the muscle
2) Sensory neurons conduct action potentials to the spinal cord
3) Sensory neurons synapse with alpha motor neurons
4) Stimulation of the alpha motor neurons causes the muscle to contract and resist being stretched
What is the function of a muscle spindle?
Assist in the regulation of movement
Maintain posture
What does a Golgi Tendon Organ do?
Monitor force development in muscle by preventing muscle damage during excessive force generation
What does stimulation of Golgi Tendon Organ do?
Reflex relaxion of the muscle
How do reflex relaxation of muscle via Golgi Tendon Organ occur?
Inhibitory neurons send IPSPs to muscle alpha motor neurons
What may ability to voluntarily oppose GTO inhibition be related too?
Gains in strength with training due to increased tendon stiffness
How does a Golgi Tendon Organ work?
1) Detect tension applied to a tendon
2) Sensory neurons conduct action potentials to the spinal cord
3) Sensory neurons synapse with inhibitor interneurons that synapse with alpha motor neurons
4) Inhibition of the alpha motor neurons causes muscle relaxation, relieving the tension applied to the tendon
What do muscle chemoreceptors do?
Inform CNS about metabolic rate of muscular activity
Where are motor neurons are located?
Spinal cord
What are motor neurons responsible for?
Carrying neural messages from spinal cord to skeletal muscles
What are motor units?
Motor neurons and all the muscle fibres which it innervates
What is innervation ratio?
Number of muscle fibres innervated by a single motor neuron
How does motor control influence innveration ratio?
Low ratio in muscles involved in fine motor control
Higher ratio in muscles that do not require fine motor control
What are the different types of motor units?
Type S (slow) or type 1 fibres (SMALLEST)
Type FR (fast, fatigue resistant) or type IIa fibres (INTERMEDIATE)
Type FF (fast, fatigable) or type IIx fibres (LARGEST)
What are 3 key components of the brain?
Cerebrum or cerebral cortex
Cerebellum
Brainstem
What does the cerebrum or cerebral cortex do?
Organization of complex movement
Storage of learned experiences
Reception of sensory information
What does the cerebellum do?
Implicated in control of movement and integration of sensory information
What does the brainstem do?
Role in cardiorespiratory function, locomotion, muscle tone, posture, receiving information from special senses
What makes up the brainstem?
Midbrain (Mesencephalon)
Medulla Oblongata
Pons
What does the midbrain do?
Connects the pons and cerebral hemispheres
Functions include
- Controlling responses to sight
- Eye movement
- Pupil dilation
- Body movement
- Hearing
What does the medulla oblongata do?
Involved in control of autonomic function, relaying signals between the brain and spinal cord and coordination of body movements
What does the Pons do?
Involved in sleep and the control of autonomic function
Relays sensory information between the cerebrum and cerebellum
What ae the 3 neurons in the spinal cord?
Motor neurons
Sensory neurons
Interneurons
What is spinal tuning?
Intrinsic neural networks within spinal cord that refine voluntary movement after receiving messages from higher brain centres
What is withdrawal reflex?
Occurs via a reflex arc, whereby a reflex contraction of skeletal muscles can occur in response to sensor input and is not dependent on the activation of higher brain centres
Means of removing a limb from a source of pain
When controlling voluntary movement, what does the spinal mechanisms do?
Results in refinement of motor control
When controlling voluntary movement, what does feedback from proprioceptors do?
Allows for further modification in motor control
When controlling voluntary movement, what does the motor cortex do?
Receives inputs from variety of brain areas including basal nuclei, cerebellum, thalamus
