The senses Flashcards
Cutaneous Receptors
for touch
nociceptors
These are specialized sensory neurons that detect painful stimuli
Somatosensation
sensation is split into consius and uncounsous
concuss
proprioception and exteroception
uncoutious
enteroception and proprioception
what are the receptors
o Mechanoreceptors
Cutaneous,
Proprioception, force
o Thermoreceptors
Temperature
o Nociceptors
Pain
Merkel cells
found om glamorous or hairless skin, detect light touch and PRESSURE
where can these receptors be found?
- Skin
Tactile, thermoreceptors, pain - Muscle
Muscle spindle - Joints
Articular
there was a diagram provides and from this cells were identified- A Merkel disc
A merkel disc consistes of
Merkel Cell – A modified epithelial cell that detects mechanical stimuli.
Afferent Nerve Ending – A sensory nerve fiber that transmits signals to the central nervous system.
Meissner’s Corpuscles
Meissner’s corpuscles are specialized mechanoreceptors found in the glabrous (hairless) skin that detect light touch and low-frequency vibrations.- made of stacked swhannn cells
Pacinian corpuscles
are specialized mechanoreceptors that detect deep pressure and high-frequency vibrations.
Ruffini endings
are specialized mechanoreceptors that detect skin stretch and sustained pressure.
Merkel Discs (Merkel Cells) are what kind of adapting?
slow adapting
Ruffini Endings are what kind of adapting
slowly adapting
what kind of adapting is messiniers courpsule
rapidly adapting
Meissner’s corpuscles are located where?
located in hands/feet
touch, vibration (5-50 Hz)
rapidly adapting
what about Pacinian Corpuscles what do they do?
high frequency vibration (300 Hz)
rapidly adapting
what is the difference between messiners corpuscles and Pacinian corpuscles?
Massiners are 0.5-1 mm
deep
Pacinians are 2- 3 mm deep
What is the two point discrimination test
The ability to distinguish between two
stimuli that are applied at close distances.
This varies in different parts of the body.
where is the most sensitive place on the body for the two point test?
Palms of the hands and
face
how do we know that the hand is sensitive?
250,000 nerve fibers to
mechanoreceptors; 17,000 of these in the hand
what is an important feature of cutaneous receptors?
Cutaneous input from the feet has an
important role in posture and balance
why is the back less sensitive to water droplets?
On limbs (except palms) and body wall
the receptive fields of Pacinian and Ruffini endings are very large.
what types of hairs receive responses?
o-hairs and D-hairs
The hairs of the body are what?
rapidly adapting and low threshold
What are C fibres LTMs
For Touch , slow adapting and low threshold for pleasant contact
what are machanico-noiceptors polymodal noichiceptoers
they are used for injurious force Slow adapting , High thereshold
what is important about motor neurons?
only nerve fibers from muscle spindles
(1a afferents) synapse directly with
motoneurons
what is the Descending Corticospinal Pathway
The corticospinal pathway carries the motor commands from the motor cortex to the muscles needed for the grip.
during grip what sends feedback about muscle strength?
Muscle Spindles and Golgi Tendon Organs in the muscles provide feedback about the muscle length and tension
Ascending Lemniscal Pathway
The lemniscal pathway carries information to brain about touch, pressure, and proprioception (the sense of where your hand is in space).
the adjustment for grip strength is done by what?
Based on this feedback, the brain sends adjustment signals back through the motor cortex, via the corticospinal pathway, to fine-tune the grip
what is the somatosensory cortex?
where the brain processes the sensory input (e.g., texture, pressure, and proprioception).
How the Thalamus Works in Sensory Processing?
When sensory information (e.g., touch, temperature, pressure) is gathered from receptors in the skin or muscles, it travels up the spinal cord.
The thalamus, located in the brainstem, acts as a relay station that filters and relays the sensory signals to the somatosensory cortex in the parietal lobe of the brain.
Brodmann Areas
Area 3,1,2 : Primary
Somatosensory cortex
Area 4: Primary Motor
Cortex
what did Wilder Penfield do?
Penfield’s most famous achievement was creating a map of the somatosensory and motor cortices of the brain, called the “motor homunculus” and “sensory homunculus”
what happens to Cortical representation throughout life? Why is it deemed static?
Is not static
through life but modifiable through
changing input and learning
merizech
He is particularly known for his groundbreaking work on how the brain is capable of reorganizing itself.Progressive change in cortical
representation after transection of
the median nerve
Sensory cancellation of tactile sensation
the brain suppresses some information in order to focus on other stimuli or avoid overwhelming sensory information eg Humans: Why can’t we tickle ourselves? Brain cancels out predictable touches
coronary discharge
When you move your eyes or head, the image on your retina changes. To keep your vision stable, your brain sends a signal (corollary discharge) that tells your visual system, “Hey, this movement is coming from me!” This prevents you from feeling like everything is shifting around randomly.
It’s like the brain is saying, “I moved, so the shift in what I see is normal, not something that should surprise me.”
what is the primary endings
Primary endings are type Ia afferent fibers that wrap around the central part of the muscle spindle fibers. They are responsible for detecting changes in muscle length and how fast those changes are happening.
Ia Afferent
Ia afferent fibers carry sensory information from muscle spindles to the brain, specifically about how much a muscle is stretched and how fast it’s changing
Alpha motor neurons
Are a crucial part of the nervous system that are responsible for controlling voluntary muscle contraction.
gamma motor neurones
are a crucial part of the nervous system that are responsible for controlling voluntary muscle contraction.
The sensory-motor system is a critical part of the nervous system
that integrates sensory input (information from the environment and body) and translates it into motor output (muscle movements).
Cortical areas:
Primary motor cortex M1
Premotor cortex
Supplementary motor area
S-I and S-II
PPC
Sub-cortical areas:
Cerebellum
Basal Ganglia
Main Descending Motor Pathways:
Corticospinal Tract (Pyramidal Tract), Extrapyramidal Tracts,
Rubrospinal Tract,
Reticulospinal Tract,
Outline Rubrospinal Tract:
Origin: The red nucleus in the midbrain.
Function: It plays a role in controlling muscle tone and coordination of limb movements, especially in the upper limbs.
Decussation: It crosses over in the midbrain
Vestibulospinal
Vestibulospinal Tract:
Origin: The vestibular nuclei in the medulla (brainstem).
Function: This pathway is important for maintaining balance and posture. It helps coordinate movements that keep the body upright, especially in response to changes in head position (like when you’re balancing or walking).
Decussation: The lateral vestibulospinal tract does not cross (uncrossed), while the medial vestibulospinal tract does cross over at the level of the brainstem.
Tectospinal Tract:
Origin: The superior colliculus (a part of the midbrain involved in visual processing).
Function: It helps coordinate movements in response to visual stimuli, especially head and neck movements in response to visual cues (like turning your head to look at something).
Decussation: It crosses over at the level of the midbrain
Motor Prediction: predicting
our actions
The ability of the CNS to
anticipate the consequences of
action is critical for the control of
voluntary action
what are Command neurons?
Term introduced by Wiersma (1964), When stimulated these neurons
evoked a movement, the pattern
of which was NOT coded in their
sequence of spikes
Neural decision-making cells
what ones are involved in forward prediction?
Prefrontal Cortex (PFC), Motor cortex, cerebellum
Command neurons in the mouse
Brainstem neurons were found
to be responsible for stopping
locomotion
* The neurons could ‘command’
the rhythmic neural circuits
(the CPG) to stop locomotion
the neurogenerative disseises effect what?
the basal ganglia
what si the basal ganglia?
Brainstem neurons were found
to be responsible for stopping
locomotion
* The neurons could ‘command’
the rhythmic neural circuits
(the CPG) to stop locomotion
Cortico-basal-thalamocortical loops:
the motor loop
motor cortex–> patamen–> lateral GPi —> ventral lateral neuculas
Executive loop
Dorsolateral prefrountal cortex —> Dorsolateral coaudate —-> Medial GPi —> medial dorsal and ventral anterior neucai
limbic loop
Anterior cingulate cortex —> ventral striatum —> ventral pallidum —-> medial dorsal nucleas
describe the basal ganglia motor loop?
Results in the activation of the supplementary
motor area (SMA) before and during
movement.
* SMA activity prior to movement: the
‘readiness potential’
* Function: sequencing of serial order actions
for the execution of learned motor programs.
* Direct and Indirect pathways: Go v No Go
The Direct Pathway: Go
excites the motor cortex,
5 neurons-
1. Corticostriate fibres from sensorimotor
cortex activate GABAergic spiny neurons in
the striatum with D1 class dopamine
receptors. These neurons are receiving
nigrostriatal input
2. Activated GABAergic striatal neurons inhibit
internal pallidal GPi neurons
4. Activation of the supplementary motor area
(SMA)
5. Modification of corticostriate activity and
initiation of movement via corticospinal
(CST) and corticoreticulospinal tracts (CRT)
Indirect Pathway ‘no go’
7 neurons
1. Corticostriate fibres from sensorimotor
cortex activate GABAergic spiny neurons in
the striatum with D2 class dopamine
receptors. These neurons are receiving
nigrostriatal input.
2. Activated striatal neurons inhibit external
pallidal GPe neurons.
3. The subthalamic nucleus (STN) receives input
from the GPe neurons
4. The STN excites the internal pallidal
neurons (GPi)
5. Inhibition of ventral lateral nucleus (VLN)
thalamocortical neurons
6. Activation of the SMA (reduced due to 5)
7. Modification of corticostriate activity and
initiation of movement via corticospinal
(CST) and corticoreticulospinal tracts (CRT)
Parkinson’s Disease Symptoms - Tremor:
dysfunction in 2 circuits the basal ganglia
and the cerebello-thalamo-cortical pathway
Rigidity:
Lead Pipe’ rigidity, Co-contraction of prime
movers and agonists, dysfunction related to golgi
tendon organs (1b) autogenic inhibition
Akinesia/Bradykinesia:
Weakened contribution of
the SMA prior to movement
Posture:
Impaired in anticipatory postural
adjustments
How is movement sculpted?
Basal Ganglia direct and
indirect pathways compete
to either facilitate or inhibit
movement
* Disinhibition of the
thalamus (Direct pathway) is
opposed by inhibition of the
thalamus by additional
excitatory circuitry from the
STN to the GPi)
movement is then explained as how Parkinson’s Disease and Huntington’s Chorea
chorea- excessive movements- Overactivity
of the Direct Pathway
Parkinson’s disease-Overactivity
of the Indirect Pathway
mirror neurons
Mirror neurons are a special type of brain cell that fires both when you perform an action and when you observe someone else performing the same action. This means that the same neural circuits are active whether you’re doing something yourself or just watching another person do it.
