PHGY 209 Sensory, motor and cognitive

What is afferent?

cell bodies out of the CNS (sensory input)

What is efferent?

cell bodies in the CNS (motor in output)

What is the somatic efferent?

1-innervates skeletal muscle 2-only excitatory (Ach) 3-motor neurons

What is the autonomic efferent?

1-innervates interneurons 2-Smooth and cardiac muscle 3-excitatory and inhibitory

Describe the brain anatomy

What is the brainstem?

what the spinal cord becomes and it contains the medulla, pons and midbrain

What does the central sulcus separate?

the motor cortex from the primary somatosensory cortex

Why is the cortex so wrinkled?

to increase the surface area of the brain since there is a limit on size

What contains the spinal fluid?

ventricles

What is the difference between the limbic system and the basal nuclei?

1- limbic system is involved in emotion and memory 2- basal nuclei is involved in motor control

What are the divisions of the spinal cord?

cervical, thoracic, lumbar, sacral, coccygeal

What receives sensory inputs?

dorsal horn

What sends motor outputs?

ventral horn

What has to be cut in order to loose all sensory information?

Dorsal root

What are the 2 main cranial nerves?

1- olfactory 2- optic

What eventually develops into the CNS?

neural plate

When does the neural plate appear?

week 3

What becomes the CNS and PNS?

ectoderm

What becomes muscle and bone?

mesoderm

What becomes the digestive tract?

endoderm

What is the dura?

covering of the brain and spinal cord

What does the cavity of the neural tube become?

ventricles and the central canal

How much cerebrospinal fluid do the ventricles contain?

150 ml

What makes CSF?

choroid plexus

How many ventricles does the choroid plexus have?

4 but production comes mainly from the lateral ventricles

At what rate is CSF produced?

500ml/day

What are the 3 functions of CSF?

1- support and cushion the CNS 2- provide nourishment to the brain 3- remove metabolic waste thru absorption at the arachnoid vili

What is the composition of the CSF?

sterile, colourless, acellular fluid that contains glucose

Is the circulation of CSF active or passive?

passive

Where does CSF circulate?

Ventricles and subarachnoid space surrounding the CNS

How does the arachnoid vili work?

collects the CSF and dumps it into the venous blood supply

What are the 2 types of hydrocephalus?

communicating and non-communicating

Where does the CSF return to the blood?

at the dural sinus

What is the only substrate metabolized by the brain?

glucose

Why does the brain need continuous supply of glucose?

very little glycogen in the brain

Does glucose transport to the brain require insulin?

no

What can result if the brain looses blood supply?

loss of consciousness and neuronal death

What percentage of blood does the brain receive?

15%

What is the function of the circle of willis?

is a safety factor that makes sure that if one side of the artery is compromised, the other can take over and maintain blood supply

Describe the circulation of blood to the brain

1- heart 2- vertebral and carotid arteries 3- circle of willis via the basilar artery 4- brain 5- venous system

Describe the circulation of CSF

1- heart 2- choroid plexus 3-subarachnoid space via ventricles 4- dural sinus via arachnoid villi 5- venus system

What lines the capillaries of the blood-brain barrier?

foot processes of astrocytes

What are examples of elements that are lipid soluble to the blood brain barrier?

alcohol and caffeine

Give an example of a substance that can't pass the blood brain barrier

morphine

How does morphine cross the blood-brain barrier?

by conversion to heroin and once inside body turns back to morphine and hard to get out

What are 5 functions of astrocytes in the blood-brain barrier?

1-maintain extracellular space 2- take up excess glutamate 3-induce tight junctions 4- regulate [K+] 5- provide structural support

What are astrocytes NOT?

neurons, they produce the phagocytosis of debris

What is sensation?

awareness of sensory stimulation

What is perception?

the understanding of a sensation's meaning

What is the law of specific nerve energies?

specificity of receptors for a particular stimulus type.

What is the law of projection?

Regardless of where in the brain you stimulate a sensory pathway, the sensation is always felt at the sensory receptors location

What is modality?

type of stimulus

How do sensory receptors work?

1- stimulus energy 2- receptor mm 3- transduction 4- ion channel activation 5- afferent

What is transduction?

conversion of stimulus energy into the opening and closing of ion channels

What is an afferent neuron?

neurons with cell bodies outside the CNS that send their axons in the CNS

How is stimulus energy converted into afferent activity?

1- stimulus energy 2- receptor potential 3- AP 4- propagation of AP 5- release of neurotransmitter

What encodes the strength of a signal?

frequency of APs

What is enough for transduction?

subthreshold

What allows us to be sensitive to changes in sensory input?

adaptation

What does the afferent response encode?

1- stimulus intensity 2- slow changes

What is a receptive field?

region in space that activates a sensory neuron or receptor

How does stimulus location affect the receptive field of the afferent response?

periphery has less APs

What is needed to produce a population code?

overlap of receptive fields

How can you tell where the stimulation is and its strength?

by activating peripheric fields

What is acuity?

ability to distinguish one stimulus from another

How are receptive fields and acuity related?

1- small RF=high acuity 2- large RF=low acuity

What is lateral inhibition?

signals from neurons at the center of the receptive field inhibit neurons on the periphery

How is lateral inhibition related to acuity?

it sharpens it

What mechanisms shape sensory information?

bottom up and top down

What kind of axons do neurons in the CNS have?

descending

Name 2 ways descending pathways can influence sensory information

1- directly inhibiting the central terminals of the afferent neuron (presynaptic inhibition) 2- via an interneuron that affects the ascending pathway by inhibitory synapses

What kind of receptor mediates touch?

mechanoreceptors with specialized end organs that surround the nerve terminal

What is the purpose of these end organs?

allow selective mechanical info to activate the nerve terminal

What are 2 superficial layers of glabrous skin?

1- meissner's corpuscle 2- Merkel disk

What are the characteristics of meissner's corpuscle?

1- fluid filled structure enclosing the nerve terminal 2- rapidly adaptive 3- light stroking and fluttering

What are the characteristics of Merkel disk?

1- small epithelial cells surrounding the nerve terminal 2- slowly adapting 3- pressure and texture

What are 2 deep layers of glabrous skin?

1- pacinian corpuscle 2- ruffini endings

What are the characteristics of pacinian corpuscle?

1- large concentric capsules of connective tissue surrounding the nerve terminal 2- rapidly adapting 3- strong vibrations

What are the characteristics of ruffini endings?

1- nerve endings wrap around a spindle-like structure 2- slowly adapting 3- stretch

How are mechanoreceptors activated?

by stretching the cytoskeletal strands which in turn forcibly opens the ion channel

What is proprioception?

sense of body position and movement with the help of muscle spindles

What receptors detect temperature?

thermoreceptors

What is a thermoreceptor?

receptor with free nerve endings containing ion channels that respond to different T ranges

Name 2 types of thermoreceptors

1- cold afferents 2- warm afferents

What chemical can activate cold afferents?

menthol

What chemicals can activate warm afferents?

1- capsaicin 2-ethanol

What receptors respond to pain?

nociceptors

What are nociceptors?

receptors that are free nerve endings containing ion channels that open in response to intense mechanical deformation, excessive T or chemicals associated with tissue damage

What are visceral pain receptors activated by?

inflammation

Name the 3 things that increases nociceptor sensitivity

1- branches on the afferent release substance P on mast cells that in turn release histamine and increase the sensitivity of nociceptors 2- local release of chemicals of damaged tissue increases sensitivity 3- Release of substance P on blood vessels around damaged tissue causes dilation which increases sensitivity

What is hyperalgesia?

increased sensitivity to pain

What are the dorsal columns?

collections of axons that go up the spinal cord carrying signals of touch and proprioception

Where do sensory neurons enter the spinal cord?

dorsal root

Where do sensory neurons synapse?

medula (ipsilateral)

Where is the second synapse of the sensory neuron?

thalamus and projections are sent to the somatosensory cortex (contralateral side)

What do the anterolateral and the dorsal column systems have in common?

cross from the side where the afferent neurons enter the CNS to the opposite side either in the spinal cord (anterolateral) or brainstem (dorsal column)

Where do the sensory pathways from the somatic receptors on the left side of the body end up?

in the somatosensory cortex of the right cerebral hemisphere

What is the anterolateral system?

The pain and temperature pathway for the body.

Where does the ascending anterolateral pathway make its first synapse?

between the sensory receptor neuron and a 2nd neuron located in the grey matter of the spinal cord

Where does the ascending anterolateral pathway make its second synapse?

second neuron crosses to the opposite side and in the thalamus where it synapses of cortically projecting neurons