Sensory function Flashcards
What are sensory pathways?
routes by which info received by different parts of the body are conveyed to the sensory cortex in the brain
What are sensory pathways also known as?
Ascending pathways
Where is the primary sensory cortex?
In the post-central gyrus
What does the primary sensory cortex feel?
Pain, pressure, or temperature in the appropriate area of the sensory cortex
What is a dermatome?
An area of skin innervated by a pair of left and right dorsal roots. Each segment of the spinal cord corresponds with one dermatome
How can dermatomes be grouped?
By the region of the spinal cord that innervates them
What is exteroception?
Sensation arising from outside the body
How does the body sense exteroception?
- somatosensory receptors on body surface or linings (touch, temp, pain, pressure)
- special sensory receptors from special sense organs (tongue, nose, eyes, ears)
What is proprioception?
Receptors in muscles, joints, and tendons which continuously convey info to the brain about location, orientation, and movement of the body
What receptors sense viscerosensation?
- mechanoreceptors
- chemoreceptors
- nociceptors (sense internal pain)
What is the direction of the sensory pathways?
Always afferent and ascending from the receptor to the sensory cortex
What are the neurons the somatosensory pathways use?
- first order neurons
- second order neurons
- third order neurons
What are first order neurons?
the sensory component of a spinal nerve which convey info from the receptor to the central nervous system
What do second order neurons do?
convey info from lower areas of the CNS to the thalamus of the opposite side
Where is the thalamus loocated?
in the diencephalon
What is decussation?
Crossing over of neurons which allows contralateral control
Where does sensory decussation occur?
in the medulla or spinal cord
What do third order neurons do?
convey infofrom thalamus to the sensory cortex
What happens when exteroceptive info reaches brain?
Sensory info that reaches consciousness without knowing the source. We are aware of it but need the sensory association cortex to interpret and make sense of it
What happens when viscerosensation reaches the brain
May reach consciousness, but is poorly localised. Many aspects do not reach consciousness
What is white matter made up of?
axons
What is grey matter made up of?
cell bodies, dendrites, and synapses
What does each spinal nerve consist of?
- a dorsal root going to the dorsal horn
- ventral root going out of ventral horn
What does the dorsal root do?
Carries sensory neurons in from that region of the body. The cell bodies are outside the spinal cord and form the dorsal root ganglion
What does the ventral root do?
Carries the motor neurons out of that region of the body
What are the somatosensory pathways known as?
- the anterolateral pathway
- the dorsal column pathway
What can the anterolateral pathway be broken down into?
- the anterior and lateral spinothalamic tracts
- the spinoreticular tracts
What does the dorsal column pathway do?
Carry fine touch, texture, vibration, pressure, and proprioceptive info
What does the anterior anterolateral spinothalamic tract do?
Carries info about non-discriminative touch and temperature
What does the lateral anterolateral spinothalamic tract do?
carries info about sharp pain and temperature
What does the spinoreticular tract do?
Carries info about pain perception
What is the order of the spinothalamic pathways?
- first order neurons synapse in dorsal horn of same side of spinal cord
- second order decussate spinal cord to the white matter of the spinal cord on the other side
- ascend to thalamus and synapse
- go onto somatosensory cortex
What is the order of the spinoreticular pathways?
- first order neurons synapse in dorsal horn of same side of spinal cord
- second order decussate spinal cord to the white matter of the spinal cord on the other side
- ascend to reticular formation in medulla and synapse
- ascend to thalamus and synapse
- ascend to somatosensory cortex
What is unique about the spinoreticular pathway?
it uses 4 order neurons instead of three
What is the order of the dorsal column pathways?
- primary afferent neurons pass into dorsal white matter on same side without synapsing
- ascend to dorsal column nuclei in posterior aspect of medulla
- synapses with an a neuron that will ascend to the thalamus
- decussates to opposite side
- ascends in the medial lemniscus tract
- to the thalamus and synapses
- then to the sensory cortex
What happens if there is damage or disease to primary sensory neurons?
- the region of the cortex that normally receives input doesn’t receive it
- may result in loss of sensation from that area
What is damage to primary sensory neurons known as?
peripheral nerve disease
What happens if there is damage to brainstem neurons or second order neurons?
Causes loss of sensation from the body from below the lesion on the opposite side
What happens if there is damage to the spinal cord?
- if damaged only on one side, touch, pain, and temp is lost from the opposite side
- proprioceptive info on the same side is also lost
