Week 3 - Nervous System (Central) Flashcards
Describe the functions of the nervous system
Control internal environment
Voluntary movement
Spinal cord reflexes
Assimilation of experiences for memory and learning
Define the anatomical division of the nervous system
Central nervous system (brain & spinal cord)
Peripheral system (neurons outside the CNS)
Sensory division (afferent fibres transmit impulses from receptors to CNS)
Motor division (efferent fibres transmit impulses from CNS to effector organs)
What is the structure of a neuron
Axon (Carriers electrical message away from cell body) (Covered by schwann cells)
Synpase (Contact points between axon of one neuron and dendrite of another neuron
Greater the diameter of axon or myelin sheath = greater neural transmission
Define resting membrane potential
The electrical charge difference between neurons inside the cell and on the exterior of the cell.
What is the magnitude of the resting membrane potential determined by
Permeability of plasma membrane to ions
Difference in ion concentrations across membrane
Na, Cl, & Ca more concentrated in extracellular fluid, K more concentrated in intracellular fluid
Describe the sodium & potassium exchange in neurons
Maintained by a pump that moves 2K in and 3Na out, helping to regulate the cell’s internal environment
What is an action potential
it occurs when a stimulus depolarises the cell, allowing Na to enter and causing a temporary positive charge inside the cell
Define the role of neurotransmitters
Chemical messenger released from presynaptic membrane
Binds to receptor on postsynaptic membrane
Causes depolarisation of postsynaptic membrane
What is the different between excitatory and inhibitory neurotransmitters
EPSP can promote neural depolarisation (temporal (single) & spatial (several) summation)
IPSP causes hyperpolarisation (neurons with more negative membrane potential resist depolarisation)
Define proprioception
Proprioception is the sense of the body’s position in space based on specialised receptors that reside in the muscles, tendons and joints. Some sensors that provide information include joint angle, muscle length, and muscle tension.
How do muscle spindles respond to changes in muscle length
- Muscle spindles detect stretch of muscle
- Sensory neurons conduct action potentials to the spinal cord
- Sensory neurons synapse with alpha motor neurons
- Stimulation of the alpha motor neurons causes the muscle to contract and resist being stretched
How does the golgi tendon organ prevent muscle damage
- Golgi tendon organ detects tension applied to tendon
- Sensory neurons conduct action potentials to the spinal cord
- Sensory neurons synpase with inhibitory interneurons that synapse with alpha motor neurons
- Inhibition of the alpha motor neurons causes muscle relaxation, reliving the tension applied to the tendon
What do muscle chemoreceptors do
Muscle chemoreceptors (metaboreceptors) are sensitive to changes in the chemical environment surrounding a muscle, informing the CNS about metabolic rates of muscular activity
What is the typical structure of a motor unit
Motor neurons are located within the spinal cord. Motor unit is a motor neuron and all the muscle fibres it innervates
What is the innervation ratio
The number of muscle fibres innervated by a single motor neuron
(Low ratio in fine motor control, higher ratio in muscle that do not require motor control)
How does motor unit recruitment occur
Recruitment of additional muscle fibres occur by activating more motor units
Recruitment pattern during incremental exercise (Type I –> Type IIa –> Type IIx)
What are the key components of the brain
Cerebrum (cerebral cortex): Organisation of complex movement, storage of learned experiences, reception of sensory information
Cerebellum: Implicated in control of movement and integration of sensory information
Brainstem: Role in cardiorespiratory function, locomotion, muscle tone, posture, receiving information from special senses
What are the key components of the brainstem
Midbrain: Connects the pons and cerebral hemispheres. Controls responses to sight, eye movement, pupil dilation, body movement and hearing.
Medulla Oblongata: involved in control of autonomic function, relaying signals between the brain and spinal cord and coordination of body movements
Pons: Involved in sleep and control of autonomic function. Relays sensory information between cerebrum and cerebellum
What types of neurons are located in the spinal cord
Motor neurons
Sensory neurons
Interneurons
What does spinal tuning mean
Spinal tuning refers to intrinsic neural networks within spinal cord that refine voluntary movement after receiving messages from higher brain centres
Describe the steps in withdrawal reflex
- During the withdrawal reflex, sensory neurons from pain receptors conduct action potentials to the spinal cord
- Sensory neurons synapse with excitatory interneurons that are part of the withdrawal reflex
- The excitatory interneurons that are part of the withdrawal reflex stimulate alpha motor neurons that innervate flexor muscles, causing withdrawal of the limb
- Collateral branches of the sensory neurons also synapse with excitatory interneurons that cross to the opposite side of the spinal cord as part of the crossed extensor reflex
- The excitatory interneurons that cross the spinal cord stimulate alpha motor neurons supplying extensor muscles in the opposite limb, causing them to contract and support body weight during the withdrawal reflex
What do muscle spindles consist of
Intrafusal fibres
Gamma motor neurons
Stretch reflex
What are the aspects of the control of voluntary movement
Motor cortex receives inputs from variety of brain areas including basal nuclei, cerebellum, thalamus
Spinal mechanisms results in refinement of motor control
Feedback from proprioceptors allows for further modification in motor control
What is the structure and processes leading to voluntary movement
Structure:
Higher brain centres -> cerebellum -> thalamus -> motor cortex - > motor unit
Step in movement plan:
Initial drive to move -> movement design -> refined movement design -> relay station -> final executor of motor plan -> execution of desired movement
