Week 3 - Central Nervous System Flashcards
4 functions of the central nervous system
1) Control of the internal environment - coordinated with the endocrine system (Hypothalamus-Pituitary Axis), perceiving and responding to events in the internal/external environment.
2) Voluntary control of movement
3) Spinal cord reflexes (rapid unconscious movements such as touching hot pan)
4) Assimilation of experiences necessary for memory and learning
Draw and outline the anatomical division of the NS.
Central NS: brain and the spinal cord (protected by skull and vertebrae)
Peripheral nervous system (PNS): neurons outside the CNS. This can be divided into sensory division and motor division.
Sensory division: detects stimuli and afferent fibers transmit impulses from receptors to CNS. Can be broken down into somatic, visceral and special sensory.
Motor division: efferent fibers transmit impulses from CNS to effector organs. Broken down into somatic and autonomic.
Autonomic: parasympathetic and sympathetic NS
Describe the role of dorsal root and ventral roots and how they differ?
To connect the nerve fibers from the PNS to the CNS
Dorsal roots are afferent - meaning they carry sensory information to the CNS (spinal cord) from the PNS
Ventral roots are efferent - meaning they carry motor information from the CNS (spinal cord) to the PNS
They both make up 31 pairs of spinal nerves in the PNS.
Define somatic sensory and visceral sensory.
Somatic - sensory input consciously perceived from receptors like the eyes, skin…
Visceral - sensory input that is not consciously perceived from receptors of blood vessels and internal organs such as the heart (e.g. increased HR).
Define autonomic and somatic NS.
Autonomic - motor output that is involuntarily controlled; effectors are cardiac muscle, smooth muscle and glands.
Somatic - motor output that is voluntarily controlled; effectors is skeletal muscle.
Dendrites
extend from the cell body and receive information from the synaptic terminals of adjacent cells
What is the role of myelin?
it enhances the conduction of an AP along a nerve fiber + insulates the axon and reduces the loss of the electrical impulse.
Axon
carry electrical messages (APs) away from the cell body
What is the role of Schwann cells in the structure of a neuron?
The cell membrane of Schwann cells is responsible for the myelination of axons.
What two factors are responsible for a greater speed of neural transmission (conduction velocity)?
- The diameter of the axon
- The amount of myelin sheath
Resting membrane potential
the electrical charge difference in the cell (intracellular) and outside the cell (extracellular)
there is a negative charge inside the cell in respect to the charge outside the cell at rest
What is the magnitude of the resting membrane potential determined by?
- Permeability of plasma membrane to ions - when channels are open ions go from an area of high conc to low conc, membrane far more permeable to K+.
- Difference in ion concentrations across the cell membrane (Na+ greater outside cell, K+ greater inside cell)
Why do we have a negative membrane potential in the cell/neuron at rest?
- Diffusion of potassium out the cell.
- Higher permeability of the plasma membrane for potassium compared to sodium
At rest, most of the sodium channels are closed whereas the potassium channels are open. Therefore, potassium ions move from high conc (in the cell) to low conc (extracellular fluid) and this net loss of positive charge leads to a negative charge which is the resting membrane potential.
How do we maintain this negative resting membrane potential?
Sodium-potassium ATPase pump
What does the sodium-potassium pump do?
Uses energy from ATP to maintain this intracellular and extracellular environment by pumping 3 Na+ OUT of the cell and 2 K+ IN the cell.
When does an action potential occur/fire? What does this result in?
It occurs/fires when an excitatory stimulus of sufficient strength (causes membrane potential increase to -50mV) depolarizes the cell by opening sodium channels.
Therefore, sodium diffuses into the cell which makes the cell more positive (depolarizing it).
K+ channels also open but K+ permeability is relatively smaller and lasts longer.
What is the threshold potential for an AP to fire?
-50mV is the voltage at which Na+ channels open to initiate AP
Repolarization
return to resting membrane potential - potassium leaves the cell rapidly and sodium channels close.
All-or-none law
Once a nerve impulse (AP) is initiated, it will travel the whole length of the axon. When the AP reaches the end, a neurotransmitter is released into the synpase.
a) Membrane potential depolarizes from -.. mV to +.. mV
b) Membrane potential repolarizes from +.. mV to -.. mV
c) The RMP of a healthy neuron is usually in the range of -..mV to -..mV.
a) -70mV to +30mV
b) +30mV to -70mV
c) -70mV to -80mV
Synapse
gap between the presynaptic neuron and the dendrites of the postsynaptic neuron
Neurotransmitters
Chemical messengers released from presynaptic membrane (in vesicles) into the synaptic cleft.
They bind to receptors on the postsynaptic membrane which causes the depolarization of the postsynaptic membrane if sufficient amounts of the neurotransmitter is released (threshold point met)
Two types of neurotransmitters
1) Excitatory neurons that produce excitatory postsynaptic potentials (EPSP) (e.g. Glutamate)
2) Inhibitory neurons that send inhibitory postsynaptic potentials (IPSP) (e.g. GABA)
What are the two ways that EPSPs can promote neural depolarization?
1) Temporal summation: rapid, repetitive excitation from a single excitatory presynaptic neuron
2) Spatial summation: summing EPSPs from several different presynaptic neurons
What are neurotransmitters that cause the depolarization of membranes called?
excitatory neurotransmitters
What do Inhibitory postsynaptic potentials cause?
They cause hyperpolarization which is a more negative resting membrane potential therefore resisting depolarization.
If we want a neuron to move towards its threshold and pass along the AP, what is the relationship between EPSP and IPSP?
EPSPs > IPSPs
3 types of joint proprioceptors
1) Free nerve endings (receptive to touch and pressure - most abundant)
2) Golgi type receptors (found in ligaments of joints)
3) Pacinian corpuscles
2 types of muscle proprioceptors (mechanoreceptors)
1) Muscle spindles
2) Golgi tendon organs
Proprioception
the sense of the body’s position in space based on specialized receptors that reside in the muscles, tendons, and joint.
Proprioceptors
sensors that provide information about joint angle, muscle length, and muscle tension, which is integrated to give information about the position and movement of our body/limbs (known as kinesthesia).
Muscle spindles
- Define it.
- What is the main function?
- What reflex is it involved in?
- Respond to changes in muscle length.
- Main function is to assist in the regulation of movement and maintain posture.
- Involved in stretch/myotatic reflex where a stretch on the muscle causes a reflex contraction (reflex sensitivity controlled by y-motor neurons).
What do muscle spindles consist of?
Intrafusal fibers - run parallel to normal muscle fibers - extrafusal fibers.
Gamma motor neurons - stimulate intrafusal fibers to contract with extrafusal fibers.
What happens when muscle spindles detect stretch of the muscle?
- Sensory neurons conduct APs to the spinal cord to alert the CNS of a change in muscle length.
- Sensory neurons synapse with alpha motor neurons (in brain).
- Stimulation of alpha motor neurons which causes the muscle to contract and resist being stretched.
- This is known as the myotatic/stretch reflex.
Golgi tendon organ (GTO)
Type of muscle proprioceptor that monitors force development/tension in the muscle and prevents muscle damage during excessive force generation.
What does the stimulation of the Golgi tendon organ result in?
increases in muscle tension results in reflex relaxation of the muscle - inhibitory neurons send inhibitory postsynaptic potentials (IPSPs) to muscle alpha motor neurons to prevent it from firing thus reducing muscle force production.
How does improved strength from resistance training influence Golgi tendon organ (GTO)?
potential ability to opposes the GTO inhibition due to increased tendon stiffness.
What happens when Golgi tendon organs detect tension applied to a tendon?
- Sensory neurons conduct APs to the spinal cord.
- Sensory neurons synapse with inhibitory interneurons that synapse with alpha motor neurons.
- Inhibition of the alpha motor neurons cause muscle relaxation, relieving the tension applied to the tendon.
Muscle chemoreceptors (OR muscle metaboreceptors)
Sensitive to changes in the chemical environment surrounding a muscle - H+ ions (implies a change in pH), C02, K+.
Inform CNS about metabolic rate of muscular activity which is important in the regulation of CV and pulmonary responses.
Motor unit
motor neuron and all the muscle fibers it innervates
Motor neurons
- Location
- Role
- Located within spinal cord
- Responsible for carrying neural messages from spinal cord to skeletal muscles.
Innervation ratio
number of muscle fibers innervated by a single motor neuron
- Low ratio in the muscles involved in fine motor control
- Higher ratio in muscles that do not require fine motor control (large limbs)
How do we recruit additional muscle fibers?
by activating more motor units - this increased force production
The size principle
the orderly and sequential recruitment of larger motor units during exercise
smaller motor units recruited first during exercise; larger motor units recruited if we need more force.
(Type S –> Type FR –> Type FF)
3 types of motor units
1) Type S (slow) / type 1(smallest)
2) Type FR (fast, fatigue resistance) / type 2a (intermediate)
3) Type FF (fast, fatigable) / type 2x (largest)
3 functions of the Cerebrum or cerebral cortex
1) Organization of complex movement (motor cortex - voluntary movement)
2) Storage of learned experiences
3) Reception of sensory information
Other functions; memory, higher reasoning, abstract thought, audio and visual processing
3 functions of the Cerebellum (Latin for little brain)
1) Control of movement (the rate, range and direction of movement)
2) Integration of sensory information.
3) Helps maintain balance and posture
Brainstem roles
- Role in cardiorespiratory function
- Locomotion, muscle tone, posture
- Receiving information from special senses.
Explain the 3 main structures of the brainstem.
1) Midbrain (mesencephalon): connects the pons and cerebral hemispheres and functions include controlling responses to sight, eye movement, pupil dilation, body movement and hearing (top)
2) Medulla oblongata: involved in control of autonomic function, relaying signals between the brain and spinal cord and coordination of body movements. (bottom)
3) Pons: involved in sleep and control of autonomic function. Relays information between cerebrum and cerebellum. (middle)
Spinal cord
- Describe it.
- What is its role?
- What 3 neurons does it contain?
45cm long, encased and protected by vertebral column, and attaches to brain stem.
Two-way transmission of sensory information from skin, joints and muscle to the brain.
Contains 3 types of neurons: motor, sensory and interneurons.
Motor control functions of the spinal cord
- Spinal tuning:
- Withdrawal reflex
Spinal tuning
refers to intrinsic neural networks within the spinal cord that refine voluntary movement after receiving messages from higher brain centers.
Withdrawal reflex (flexion withdrawal reflex)
whereby a reflex contraction of skeletal muscles can occur in response to sensory input and is not dependent on the activation of higher brain centers (moving hand from heat).
withdrawal of a limb from a painful stimulus to protect the body from harm.
Describe the process of a withdrawal reflex.
- Painful stimulus
- Sensory neurons from pain receptors conduct APs to the spinal cord.
- Sensory neurons synapse with excitatory interneurons that are part of the withdrawal reflex.
- They then stimulate alpha motor neurons that innervate flexor muscles, causing withdrawal of the limb from the painful stimulus.
- Also associated with crossed extensor reflex to ensure balance/support of body weight.
Crossed extensor reflex
this is where the opposing limb is extended in order to be able to support body weight during the removal of that injured limb.
A “movement plan” is first developed by the ___ before being sent to the spinal centers for modification.
motor cortex
Describe the 3 levels of the control of voluntary movement.
Precommand level: Cerebellum (fast movements) and basal nuclei (slow movements) involved in planning/coordinating of movement design.
Projection level: Motor cortex receives inputs from a variety of brain areas including basal nuclei, cerebellum, and the thalamus. It sends this information to spinal cord motor neurons (motor units) which results in execution of desired movement.
Segment level: Spinal tuning occurs which results in the refinement of motor control.
Throughout this process feedback from proprioceptors allow for further modification of motor control.
What does the control of voluntary movement involve?
cooperation of many areas of the brain along with subcortical areas
Role of Astrocyte in the presynaptic terminal.
They take up excess neurotransmitters (e.g. glutamine and GABA) that doesn’t interact with receptors on the postsynaptic membrane.
What is the difference between convergence and divergence?
Convergence: when a neuron receives input from many other neurons
Divergence: neuron synapses with many other neurons
