Test 2
The somatic motor system: Basic structures and organization:
- The motor cortex contains:
o supplementary motor area
o the premotor area
o primary cortex area
o basal ganglia
o spinal pathways
o motor nerves and motor receptors
The primary motor cortex:
- located between the premotor cortex and the primary somatosensory area
- part of the brain the sends info to the rest of the body to do a movement
- where the action potentials are started
- mapped out as a homunculus
Sequence of events:
- most of the signals originate in the prefrontal cortex.
- From there it goes to the premotor cortex (it inhibits and plans out movement). If this
area is damaged, you would not be able to select the appropriate strategy for reaching
things
- It then travels to the supplementary cortex which programs the motor sequence. If there
is damage to this area, it is very awkward and they are unable to orient themselves
correctly
- Once programmed, the signal travels to the primary motor cortex to activate the
neurons that will eventually activate the muscles. It is located in the percentral gyrus.
The way it is organized is: the more cortical volume allotted to each limb/part of the
body in that cortex, the more muscles there are in that area of the body. A specific part
of the cortex will activate a specific part of the body. (homunculus)
o In the medial, there is the feet, genitals,legs etc.
o As you move outwards, there is the rest of your body
o APPLICATION: This tells us that certain areas of the brain control certain body
parts:
If there is medial damage, the feet or ankles will have difficulty moving
**all of the neurons will affect the contralateral side of your body, meaning they will affect the
opposite side of the body they start on
Corticospinal tract:
- The major motor pathway from the primary motor cortex to the motor neurons
- Begins at motor cortex, travels down to the brain stem. In the medulla 80% of the nerve
fibres cross to the other side of the body (HAPPENING IN THE BRAIN STEM) and 20% stay
on the same side. From the brain stem they go to the spinal cord until the spinal cord
synapse with the motor neurons. Here the remaining 20% of fibres that remained on the
same side cross over to the other side.
, - Motor cortex cortical spinal tract (contains brain stem and 80% of nerves cross over)
upper spinal cord lower spinal cord (where the remaining 20% of neurons cross over)
synapse alpha-motor neuron to muscle
Muscle reports:
- “muscle sense” (a.k.a. proprioception): it is important for the brain to be aware of the
position and contraction of the muscles at all time
- we have special receptors in the muscle which send signals back to the brain. These
receptors include:
o muscle spindles- detect muscle stretch, rate of change of the stretch
o golgi tendon organs- detect muscle tension
Muscle spindles:
- they detect the stretch and length of the muscle.
- Consists of:
o intrafusal muscle fibres- for proprioception (orientation)
o extrafusal fibres- for contraction of muscles
o central sensory region
o 2 sets of gamma motor neurons that activate intrafusal fibres
o sensory neuron that originates in the sensory region
- when the muscle stretches, the sensory region spindles stretch. When it does this it
depolarizes and causes an action potential in the sensory nerve and it then sends the
signal back to the brain
- proprioception: the fact that the muscle is attached to a limb and we know the position
of the limb in space
- alpha- motor neuron will activate the extrafusal neurons and allow them to contract
- the gamma motor neuron activates the intrafusal fibres to contract and it tells us how
well the contraction went.
Alpha- Gamma coactivation:
- when muscles contract, the signal is sent from the spinal cord to alpha motor neurons.
In this case only extrafusal fibres contract.
- Intrafusal fibres within the muscles slack off and the information from the muscle
spindle will stop.
- To make sure the signals keep on sending, the signals must simultaneously be sent to
alpha and gamma cells. (to cause the contraction of intrafusal fibres)
- This way, the muscle spindles will continue to send information about the muscle and
limb positions to the brain
Summary:
-alpha- motor neurons allow the extrafusal neurons to contract
- gamma neurons allow intrafusal neurons to contract- sends information back to the brain gives
us info about how well the muscle contraction went. “did it move the way we intended it to?”
- the intrafusal fibres are surrounded by extrafusal fibres
, - if the alpha motor activates only, no information from the extrafusal fibres will be sent to the
brain about whether the contraction happened correctly (because the intrafusal fibres have not
been activated)
The reflex arc:
- Requires a sensory receptor, a sensory neuron, synapses, interneurons, motor neuron
and an effector organ
- Activity begins in the receptor with a receptor potential that produces an action
potential in the sensory neuron
- The action potential enters the spinal cord and produces action potentials on the
interneurons and eventually the motor neurons.
- The motor neuron will activate the effector
The stretch reflex: sequence of events:
1) Tap on tendon produces small stretch of the quadriceps muscle
2) Stretching of the muscle stretch muscle spindles
3) Muscle spindles trigger action potential in the sensory neuron that enters the spinal cord
4) The motor nerve of the quadriceps is activated while the muscles of the hamstring are
inhibited
5) Quadriceps contract and the hamstring relaxes, the lower leg kicks out
6) ***the brain is not involved with the contraction of the muscle
Cerebellum:
- small, but contains the most neurons
- it generates accurate limb movements, corrects ongoing muscle movements, modifies
strength of reflexes, involved with Pavlovian conditioning, learning new muscle
movements, etc.
- receive information from the motor cortex about the muscles being activated, as well as
information about the position of the limbs in space.
- The cerebellum compares signals from the brain with the information from the muscle
itself. This way it can make sure the muscle is actually doing what it is supposed to do,
and if its not, the cerebellum will fix it with the signals from the primary motor cortex
The limbic system:
- Our emotional centre
- Composed of:
o Hypothalamus
o Amygdala
o Hippocampus
o Cingulate cortex
o Septum
- Key function: link higher thought processes of the brain to primitive emotional
responses
- Allows us to respond correctly to changes in our environment
The somatic motor system: Basic structures and organization:
- The motor cortex contains:
o supplementary motor area
o the premotor area
o primary cortex area
o basal ganglia
o spinal pathways
o motor nerves and motor receptors
The primary motor cortex:
- located between the premotor cortex and the primary somatosensory area
- part of the brain the sends info to the rest of the body to do a movement
- where the action potentials are started
- mapped out as a homunculus
Sequence of events:
- most of the signals originate in the prefrontal cortex.
- From there it goes to the premotor cortex (it inhibits and plans out movement). If this
area is damaged, you would not be able to select the appropriate strategy for reaching
things
- It then travels to the supplementary cortex which programs the motor sequence. If there
is damage to this area, it is very awkward and they are unable to orient themselves
correctly
- Once programmed, the signal travels to the primary motor cortex to activate the
neurons that will eventually activate the muscles. It is located in the percentral gyrus.
The way it is organized is: the more cortical volume allotted to each limb/part of the
body in that cortex, the more muscles there are in that area of the body. A specific part
of the cortex will activate a specific part of the body. (homunculus)
o In the medial, there is the feet, genitals,legs etc.
o As you move outwards, there is the rest of your body
o APPLICATION: This tells us that certain areas of the brain control certain body
parts:
If there is medial damage, the feet or ankles will have difficulty moving
**all of the neurons will affect the contralateral side of your body, meaning they will affect the
opposite side of the body they start on
Corticospinal tract:
- The major motor pathway from the primary motor cortex to the motor neurons
- Begins at motor cortex, travels down to the brain stem. In the medulla 80% of the nerve
fibres cross to the other side of the body (HAPPENING IN THE BRAIN STEM) and 20% stay
on the same side. From the brain stem they go to the spinal cord until the spinal cord
synapse with the motor neurons. Here the remaining 20% of fibres that remained on the
same side cross over to the other side.
, - Motor cortex cortical spinal tract (contains brain stem and 80% of nerves cross over)
upper spinal cord lower spinal cord (where the remaining 20% of neurons cross over)
synapse alpha-motor neuron to muscle
Muscle reports:
- “muscle sense” (a.k.a. proprioception): it is important for the brain to be aware of the
position and contraction of the muscles at all time
- we have special receptors in the muscle which send signals back to the brain. These
receptors include:
o muscle spindles- detect muscle stretch, rate of change of the stretch
o golgi tendon organs- detect muscle tension
Muscle spindles:
- they detect the stretch and length of the muscle.
- Consists of:
o intrafusal muscle fibres- for proprioception (orientation)
o extrafusal fibres- for contraction of muscles
o central sensory region
o 2 sets of gamma motor neurons that activate intrafusal fibres
o sensory neuron that originates in the sensory region
- when the muscle stretches, the sensory region spindles stretch. When it does this it
depolarizes and causes an action potential in the sensory nerve and it then sends the
signal back to the brain
- proprioception: the fact that the muscle is attached to a limb and we know the position
of the limb in space
- alpha- motor neuron will activate the extrafusal neurons and allow them to contract
- the gamma motor neuron activates the intrafusal fibres to contract and it tells us how
well the contraction went.
Alpha- Gamma coactivation:
- when muscles contract, the signal is sent from the spinal cord to alpha motor neurons.
In this case only extrafusal fibres contract.
- Intrafusal fibres within the muscles slack off and the information from the muscle
spindle will stop.
- To make sure the signals keep on sending, the signals must simultaneously be sent to
alpha and gamma cells. (to cause the contraction of intrafusal fibres)
- This way, the muscle spindles will continue to send information about the muscle and
limb positions to the brain
Summary:
-alpha- motor neurons allow the extrafusal neurons to contract
- gamma neurons allow intrafusal neurons to contract- sends information back to the brain gives
us info about how well the muscle contraction went. “did it move the way we intended it to?”
- the intrafusal fibres are surrounded by extrafusal fibres
, - if the alpha motor activates only, no information from the extrafusal fibres will be sent to the
brain about whether the contraction happened correctly (because the intrafusal fibres have not
been activated)
The reflex arc:
- Requires a sensory receptor, a sensory neuron, synapses, interneurons, motor neuron
and an effector organ
- Activity begins in the receptor with a receptor potential that produces an action
potential in the sensory neuron
- The action potential enters the spinal cord and produces action potentials on the
interneurons and eventually the motor neurons.
- The motor neuron will activate the effector
The stretch reflex: sequence of events:
1) Tap on tendon produces small stretch of the quadriceps muscle
2) Stretching of the muscle stretch muscle spindles
3) Muscle spindles trigger action potential in the sensory neuron that enters the spinal cord
4) The motor nerve of the quadriceps is activated while the muscles of the hamstring are
inhibited
5) Quadriceps contract and the hamstring relaxes, the lower leg kicks out
6) ***the brain is not involved with the contraction of the muscle
Cerebellum:
- small, but contains the most neurons
- it generates accurate limb movements, corrects ongoing muscle movements, modifies
strength of reflexes, involved with Pavlovian conditioning, learning new muscle
movements, etc.
- receive information from the motor cortex about the muscles being activated, as well as
information about the position of the limbs in space.
- The cerebellum compares signals from the brain with the information from the muscle
itself. This way it can make sure the muscle is actually doing what it is supposed to do,
and if its not, the cerebellum will fix it with the signals from the primary motor cortex
The limbic system:
- Our emotional centre
- Composed of:
o Hypothalamus
o Amygdala
o Hippocampus
o Cingulate cortex
o Septum
- Key function: link higher thought processes of the brain to primitive emotional
responses
- Allows us to respond correctly to changes in our environment
