Sensory and Motor Systems Flashcards
Define sensation (1)
Sensation is the conscious or subconscious awareness of changes in the external or internal environment
Name the Sensory modalities (2)
- General senses
▪ Somatic senses
▪ Visceral sensations - Special senses
▪ Taste
▪ Smell
▪ Hearing and Equilibrium
▪ Vision
- Special senses receptors are located within sensory organs
Explain the series of events that leads to sensation (4)
- Stimulation of the sensory receptor (PNS)
- Transduction of the stimulus into neural signals
- Generation of nerve impulses and propagation to the CNS
- Integration by the CNS
Describe the neuron organisation of the sensory systems (order neurons) (3)
1st order neuron: from sensory receptor to spinal cord - 1st synapse
2nd order neuron: from spinal cord to thalamus
3rd order neuron: from thalamus to cerebral cortex(sensory)
Explain the differnet types of sensory receptors (3)
1st order sensory neuron w/ free nerve endings: detects stimuli (eg cold) -> nerve impulse -> propagated along axon to CNS
1st order sensory neuron w/ encapsulated nerve endings: detects stimuli (eg vibration)nerve impulse -> propagated along axon to CNS
Sensory receptor synapses w/ 1st order sensory neuron: detects stimuli/receptor potential -> excretes neurotransmitters-> nerve impulse -> propagated along axon to CNS
Where are somatosensory receptors and what do they do? (2)
▪ Somatosensory receptors are embedded in the skin, mucous membranes, skeletal muscles, tendons and joints
▪ They detect touch, pressure, stretching, temperature, pain, and vibrations.
Name + explain the some types of somatosensory receptors (5)
types:
- Tactile disc (type1): continuous touch
- Meissner corpuscle - touch onset low freq vibration
-Ruiffini corpuscle (type2) - skin stretch + pressure
-hair root plexus - hair disturbance
- pacinian corpuscle - high freq vibration
Where are propioceptors receptors and what do they do? (3)
-type of somatosensory r’s
▪ Proprioceptors are embedded in muscles and tendons
▪ They inform about muscle contraction, tension at tendons, the position of joints
▪ They include muscle spindles and tendon organs
Explain the Somatosensory pathways (4)
Somatosensory impulses ascend to the somatosensory cortex via three tracts:
1. Dorsal columns tract
2. Spinothalamic tract
3. Trigeminothalamic tract
Proprioceptive information reaches the cerebellum via the spinocerebellar tracts (not consciously perceived)
Describe the dorsal columns tract (4)
- transmit info about touch, pressure, vibration + proprioception from limbs, trunk, neck and posterior part of the head
- 1st order projects from sensory receptor to dorsal column nuclei (nucleus gracilis and cuneatus)
- 2nd order neuron decussates + project from dorsal column nuclei to ventral posterior thalamus (CROSSING OVER -> to transmit info)
-3rd order neuron projects from thalamus to primary somatosensory cortex
Describe the spinothalamic tract (4)
Transmits information about pain, temperature, itch, and tickle from the limbs, truck, neck, and posterior part of the head
- 1st order neuron projects from sensory r to dorsal horn of the spinal cord
-2nd order neuron decussates and projects from dorsal horn to VPN the thalamus
-3rd order neuron projects from the thalamus to the primary somatosensory cortex
Describe the Trigeminothalamic tract (4)
Transmit somatosensory information from the face, oral and nasal cavities and teeth.
-1st neuron projects from the sensory receptor to either the pons or the medulla.
-2nd order neurons decussate and project to VPN of the thalamus
-3rd neurons project from the thalamus to the primary somatosensory cortex
Explain the Sensory homunculus (4)
▪ The primary somatosensory cortex is located in the postcentral gyrus of the parietal lobe
▪ Each area receives sensory inputs from a different part of the body
▪ This differential representation is directly related to the density of sensory receptors in each body part
▪ It creates a distorted representation of the body known as the sensory homunculus.
What is neurosyphilis? (5)
▪ Syphilis is a sexually transmitted disease
▪ It is caused by the bacterium Treponema pallidum
▪ In third stage: affects the CNS
▪ Causes progressive degeneration of the posterior portions of the spinal cord
▪ Somatic sensations are lost.
Explain the Olfactory epithelium components (3) + formation of cranial nerve 1 (3) -CONFUSED
Smell:
- olfactory receptor cells = bipolar, meaning -> that they have two projections from their cell body:
1) dendrite extends to the surface of olfactory epithelium + expands at the epithelial surface = becomes olfactory bulb (dendrite surface)
- bulb contains cilia r’s for odour
- each r has axon extending from its basal surface to the basal surface of the olfactory cells
-located directly inferior of the cribiform plate + ethmoid bone (makes up roofy component of the nasal cavity)
2) whilst projecting to the cell body, the axon combine w/receptor cell axons = nerve bundle fibre/ olfactory nerve/cranial nerve 1
3) where it synapses, = glomeruli
-generally mitral cells responsible for processing info from the glomerular unit into the olfactory tract which will then spread along to go to the olfactory nerve
Walk through the Olfactory pathway - CONFUSED (10/11)
1) axons projecting from olfactory r’s
2) olfactory nerve
3) terminate at the olfactory bulb (main relay station for this pathway)
4) glomeruli
5) mitral relay cells
6) 2nd order neuron
7) olfactory tract
8) olfactory cortex
9) medial frontal lobe sulk - olfactory groove
10) medial dorsal nucleus (thalamus) from the olfactory tubercle -> to orbitofrontal cortex
Explain the 3 order olfactory pathway (3)
1) olfactory r synapses with olfactory bulb
2) olfactory tubercle-> thalamus MDN
3) thalamus -> orbitofrontal cortex
What is hyposmia? (3)
▪ Reduced ability to smell
Caused by aging:
▪ 50% over 65yo
▪ 75% over 80yo
Neurological changes:
▪ Head injury
▪ Alzheimer’s disease
▪ Parkinson’s disease
▪ Drugs (antihistamines, analgesics, steroids)
▪ Smoking
- COVID
What is the anatomy of taste papillae and buds? (5)
- surface of the tongue covered by a load of visible small bumps = papillae (vallate, foliate, fungiform) -TASTEBUDS on them
each tastebud:
- made-up of taste receptors cells
- supporting + basal cells = eventually taste receptor
-taste cells = lifespan of approx 2wks + the basal cells replace dying taste cells
- taste cells have microvilli = open into the taste pool -> where chemicals from the food interacts w/receptors + the taste cells
What are the 5 gustatory sensations? (5)
sweet
salty
sour
bitter
umami
Walk through the Gustatory Pathway (4) - CONFUSED
3 order neurons:
-tongue innervated by 3 cranial nerves (facial, vagal, glossopharyngeal)
1) all 3 nerves enter at the medulla
2) then sent to VPM - this is in thalamus
3) VPM - gustatory cortex
Gustatory cortex
I
VPM
I
Gustatory nucleus
I
Anterior Tongue, Posterior tongue, Epiglottis
What is taste aversion? (1)
Taste aversion is the avoidance of food that causes digestive issues
Why is important to understand taste aversion? (4)
▪ E.g. sweet taste evokes pleasure, while bitter taste evokes disgust
▪ Taste aversion may derive from the taste projections to the limbic system and hypothalamus
▪ It has survival benefits
▪ But may be wrongly associated
Describe the anatomy of the ear (3)
External ear: auricle, external auditory canal, tympanic membrane
Middle ear: malleus, incus + staples (smallest bones in ear)
Then inner ear - staples connects to oval window, which links onto the semicircle canal, cochlea + vestibule, vestibular 8 nerve (vestibular/cochlear)
Describe the auditory pathway (10)
1) external waves captured by auricle -> acoustic meatus
2) travels through tympanic brain + waves cause it to move
3) bones in the middle bones move medially but the incus moves laterally
4) = pushes long process of incus
5) = pushes stapes medially = hits the oval window
6) = large amplitude wave of low force into small amplitude vibration of a high force in the internal ear
7) = vibrates fluid in scalar vestibular
8) r’s send info via vestibulocochlear nerve to brain
9) soundwaves sent up scalar vestibule to cochlear duct
10) organ of corti convert vibrations into electrochemical signals via influx of k+ current
What will the influx of k+ cause?(1) Explain the 3 order pathway (3)
generation of local current + AP’s =>
1) sent up via vestibulocochlear nerve -> projections to medulla (ventral + dorsal cochlear nuclei)
2) V/D cochlear nuclei -> superior vestibular complex + superior olivary nucleus
3) -> primary auditory cortex
What is a Cochlear implant? (1)
A cochlear implant is a device that translates sounds into electrical signal that can be interpreted by the brain.
Describe the Vestibular apparatus (3)
Saccule + utricle have efferent fibres -> basilar membrane of hair cells
hair cells detecting oscillations = sense info = K+ opening
= AP’s will send transmit signals through efferent signals
What is the equilibrium pathway? 3 order neuron (3)
- part of vestibular branch of vestibular nerve
- synapses w/ vestibular nuclei in spinal cord (+accessory nerve, abducens nerve, trochlear nerve, oculomotor nerve)
= synapses w/ VPN = vestibular area in cerebral cortex
Describe motion sickness, including the symptoms and treatment (3)
When there is conflict between senses about motion + vision.
▪ E.g. travelling by car, boat or plane
Symptoms include: paleness, restlessness, excess salivation, nausea, dizziness, cold sweats, headache, and malaise that may progress to vomiting
Medications for motion sickness are usually taken in advance of travel and include scopolamine in time-release patches or tablets
Summary 1 (6)
- Sensory modalities can be divided into general senses (somatic and visceral senses) and special senses (senses of smell, taste, hearing, equilibrium)
- All sensory systems follow a similar organization that includes 1st, 2nd, 3rd neuron
- Somatosensory information is transmitted to the brain via the dorsal columns, spinothalamic and trigeminothalamic tracts
- Special senses travel to the brain through different neural pathways depending on the sensory modality
- All special senses (apart from olfaction) make a synaptic relay in the thalamus before reaching the cerebral cortex for conscious perception
- Understanding the neural pathways involved in the transmission of sensory information can help understand different lesions and conditions affecting the CNS
What is Voluntary movement and what is it controlled by? (2)
Premotor cortex: (in front of primary cortex)
* Broadman’s area 6
* Anterior to primary motor area
* Planning of voluntary movements
Primary motor cortex: (anterior to central sulcus)
* Broadman’s area 4
* Located on the precentral gyrus
* Execution of voluntary movements
How is the motor pathway a two stage process? (3)
primary motor cortex
1)—- upper motor neuron—-
spinal cord + brainstem
2)—- lower motor neuron—-
skeletal muscle
What are the 2 major motor pathways? (4)
Direct / Pyramidal:
Upper motor neurons from the primary motor cortex provide direct input to lower motor neurons in the spinal cord and brainstem.
-Corticospinal
-Corticobulbar
Indirect / Extrapyramidal:
Motor commands to lower motor neurons are provided by motor centres in the brainstem.
-Rubrospinal
-Tectospinal
-Vestibulospinal
-Reticulospinal
Describe the Pyramidal motor pathway via the 2 tracts (4)
1)primary motor cortex -> upper motor neuron
2a) spinal cord (corticospinal tract)
2b) brain stem (corticobulbar tract)
3a) spinal nerve - via lower motor neuron
3b)cranial nerve- via lower motor neuron
4a) skeletal muscles - limbs + trunk (arms, legs, genitals etc)
4b) skeletal muscles - head + neck (tongue, face, pharynx)
how is the info distributed in the corticospinal tract? (2)
lateral portion sends info to distal muscles
anterior portion sends info to proximal muscles
What is the Initial common path in the corticospinal pathway? (2)
In the corticospinal tract, axonal projections from upper motor neurons descend through a common path consisting of:
- Corona radiata
- Internal capsule
- Crus cerebri (midbrain)
The anatomy of the Corona radiata & internal capsule (2)
corona radiata: made out of white matter descending tracts
internal capsule: middle pathway to crus cerebri
The anatomy of the Crus cerebri (2)
- info fibres form cerebral peduncles
-after this: decussates in medulla oblongata
state which of the corticospinal tracts decussates at the pyramids (2)
anterior: ipsilateral (no decussation)
lateral: contralateral (decussates)
Summarise the overall pathway from corona radiata to pyramids (4)
1) corona radiata
2) internal capsule
3) crus cerebri
4) decussation at the medullary pyramids
What feature of the corticospinal tract enter at opposing sides? (3)
lateral = decussates
anterior = same side
lateral + anterior branches synapse w/contralateral lower motor neurons
- so anterior branch decussates in spinal cord compared to decussation in medulla for lateral
Describe the Corticobulbar tract (4)
- upper motor neurons from the head +neck area of the motor cortex send AP’s through the corona radiata + internal capsule
-upper motor neurons axonal projections establish synaptic connections w/cranial nerve nuclei neurons in the brainstem
-the axons of lower motor neurons form the motor components of the cranial nerves that innervate the head and neck
-some of the axons of the corticobulbar tract decussate
The anatomy of Cranial nerve nuclei (3)
- Cranial nerve nuclei are bilaterally located at different levels of the brainstem (midbrain, pons and medulla)
- Corticobulbar fibres bilaterally innervate most cranial nerve nuclei
- Some cranial nerve nuclei are only receiving contralateral innervation
Anatomy of Cranial nerves (5)
- Cranial nerve nuclei process sensory and/or motor info from/to the head+neck
- Cranial nerve nuclei communicate w/peripheral structures of the head+neck through different cranial nerves
- Most cranial nerves have a sensory (afferent) and motor (efferent) component
- The corticobulbar tract innervates lower motor neurons forming the motor component of most cranial nerves
each specific cranial nerves goes to specific facial or neck muscles eg oculomotor nerve to ocular muscles
Summary of pyramidal motor pathway - table (12)
Tract: Lateral corticospinal
Origin: medial motor cortex
Decussation: pyramids
Termination: limb + trunk distal muscles
Tract: anterior corticospinal
Origin: medial motor cortex
Decussation: each segment of spinal cord
Termination: limb + trunk distal muscles
Tract: Corticobulbar
Origin: lateral motor cortex
Decussation: bilateral innervation of cranial nerve nuclei
Termination: muscles of the head and neck
state the extrapyramidal motor pathway branches + function (4)
tectospinal + rubrospinal tract in midbrain
vestibulospinal tract in pons
reticulospinal in medulla
= all for posture, balance + muscle bone
Describe each tract and its origin in the extrapyramidal pathway (4 +1)
their upper neurons are in brainstem unlike pyramidal pathway:
-Tectospinal : superior colliculus
-rubrospinal: red nucleus
-vestibulospinal: vestibular nucleus
-recticulospinal: reticular formation
Anatomy of the tectospinal tract (5)
originates in the superior colliculus
crosses in the ventral tegmental decussation
terminates in cervical segments of the spinal cord
establishes synaptic connections with axial lower motor neurons innervating the head and trunk
mediates reflex movements in response to visual and auditory stimuli
Anatomy of the Rubrospinal tract (5)
- Originates in the red nucleus of the midbrain
- Crosses in the ventral tegmental decussation
- Descends ventrolaterally in the spinal cord (intermingled with the lateral corticospinal tract)
- Controls the tone of flexor muscles of the limbs
- The red nucleus receives afferent projections from the motor cortex and cerebellum (non-pyramidal route to control spinal motor activity).
Anatomy of the vestibulospinal tract (3)
Two components: lateral & medial.
- The lateral vestibulospinal tract synapses with lower motor neurons in the lumbar spinal cord involved in the maintenance of posture.
- The medial vestibulospinal tract synapses with cervical lower motor neurons that coordinate head and eye movements.
- The vestibular nucleus integrates information about equilibrium and balance from the vestibulocochlear nerve and the cerebellum.
Anatomy of the reticulospinal tract (4)
- Originates in the reticular formation of the medulla
- Acts on lower motor neurons innervating proximal muscles of the trunk and limbs
- The reticular formation receives inputs from several sources, including the cerebellum and basal ganglia.
Involved in:
* Posture
* Regulation of muscle tone during ongoing movement
Summary of Extrapyramidal
pathway
image
Summary 3 (6)
- There are two main motor pathways: pyramidal and extrapyramidal
- The pyramidal motor pathway can be divided into the corticospinal and corticobulbar tract
- The corticospinal tract is further subdivided into a lateral and anterior component, which innervate lateral and distal muscles of the trunk and limbs
- The corticobulbar tract innervates cranial nerve nuclei of the brainstem and controls muscles of the head and neck.
- The extrapyramidal motor pathway originates in the motor nuclei of the brainstem and consists of the tectospinal, rubrospinal, vestibulospinal and reticulospinal tracts
- Theses tracts modulate the activity of skeletal muscles involved in the regulation of posture, balance and muscle tone
