{Anatomy} Chapter 20: Somatic Senses + Motor Control

Sensation
Conscious or subconscious awareness of changes in external or internal conditions
For a sensation to happen, what four conditions must be satisfied?
1) A *stimulus*
2) A *sensory receptor* (converts stimulus to a nerve impulse)
3) Nerve impulses must then be *conducted* along a neural pathway from sensory receptors in brian
4) A region of the brain must receive and *integrate* the nerve impulses, producing a …sensation

Stimulus > Sensory receptor (stimulus>nerve impulse) > Conduction (nerve impulse travel) > Processing (we feel it after we process it)

What different forms can a stimulus take?
Light, heat, pressure, mechanical, and chemical
Describe how a sensory receptor converts a nerve impulse
when neurons touch sensory receptors they open doors for ions to flow through
A *perception* is the….
Conscious awarness and interpreation of a sensation
Where are perceptions integrated, or *processed* at?
The cerebral cortex
When senses differ, like pain versus pleasure, we call it….?
Sensory *Modality*
Sensory neurons are monogamous, what does this mean?
For example, pain neurons dont carry pleasure impulses
Adaption
Decrease in sensation when you;’re exposed to the same stimulus too long….hot tubs
2 classes of sensations
General and Special
$EXAM$ General sensations contains what two sub classes of sensations
Somatic (touch, pressure, vibration, cold, pain, warm, and proprioceptive) senses
Visceral senses (organs)
2 classes of sensations
General and special
Special senses include what?
Smell, taste, vision, hearing, and equilibrium (everything but touching and stuff)
Since we said sensory neurons carry only their own sensorys, theres tons of different ones. STRUCTURALLY, we can classify them as what three types???
1) Free nerve endings
2) Encapsulated nerve endings
3) Seperate cells (that synapse with sensory neurons)
or we can classify based on the TYPE of stimulus they DETECT….name the six classifcations of those
1) Photoreceptors
2) Mechanoreceptors
3) Thermoreceptors
4) Osmoreceptors
5) Chemoreceptors
6) Nocireceptors
(*T*hose *M*en *P*ee *O*n *C*ertain *N*iggs)
Define all:
1) Photoreceptors
2) Mechanoreceptors
3) Thermoreceptors
4) Osmoreceptors
5) Chemoreceptors
6) Nocireceptors
1) Photoreceptors – Light
2) Mechanoreceptors – Touch/Pressure
3) Thermoreceptors – Temp
4) Osmoreceptors – Osmotic
5) Chemoreceptors – Detect chemcals
6) Nocireceptors – Physical or chemical damage response

..detetectopm

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Finally, *location of the receptors* and their *origin* can also be used to classify…list those
1) Exteroceptors – at or near external surface of body
2) Interoceptors – IN blood vessels, muscles, or organs
3) Proprioceptors – IN muscles, tendons, joints, and inner ear
Define: Somatic sensations
Include touch, pressure, vibration, warm, cold, pain, and proprioceptive sensations
SOmatic sensations arise from the stimulation of sensory receptors embedded in the… (four places?)

soma means body so think of places you like to feel alive at…;)

1) Skin
2) Muscous membranes of MOUTH, VAGINA, and ANUS
3) Muscles, Tendons, and Joints
4) Inner ear
Sensory receptors for somatic sensations are distributed (evenly/unevenly)
Unevenly – More at tip of tongue, lips, fingertips….less at back of neck
Define: Cutaneous sensations
Somatic sensations arising at the skin surface
Somatic sensations are of four sensory *modalities*, which are what?
1) Tactile
2) Thermal
3) Pain
4) Proprioceptive
Tactile sensations include what five sensingnessnessess?

You poke yourself with a tack…

TOUCH, Pressure, VIBRATION, itch, TICKLE

You TOUCH the tack, which create PRESSURE in your finger and your eyes begin to VIBRATE with anger especially because your butt also ITCHES so you ask your sister to come in and TICKLE the itch

TOUCH, Pressure, VIBRATION, itch, TICKLE

TOUCH, Pressure, VIBRATION, are controlled, or mediated by what type of nerve?

What about itch and tickle?

Touch, Pressure, and Vibration —-> Encapsulated mechanoreceptors

Itch and Tickle —–> Free nerve endings

In terms of touch,, we can divide it into what two types?
Fine and Crude
Fine touch contains two sub-types (receptors), they are what?
Corpuscles of touch (def: hairless skin)- *Hands*, eyelids, tip of tongue, *lips*, nips, soles, clitoris, tip of penis
Type 1 Cutaneous mechanoreceptores (Merkel discs( – Fingertips, *hands*, *lips*, external genitalia
Crude touch contains what two receptors
Hair root plexuses – obvi, not obvi. These are senses located in HAIRY skin so it makes sense they’re crude cuz when you sense a Jbug on your arm it’s from the hair receptors but you dont know exactly where they jbug is at…lesbians

Type II Cut mechano (Ruffini corpuscles) – hands, have to do with *stretching*

Done with touch, now on to pressure and vibration.
Pressure.,,,,the types of receptors of pressure include what three receptors?
1) Corpuscles of touch
2) Type 1 mechano (Both of the fine touch receptors(
3) *Lamellated pacinian corpuscles*
Lamellated sounds like jello so youc an picture jello vibrating a round and the spoon on top of the jello is pushing down and creating pressure
Done with pressure, onto vibraction.

What are the types of receptors that deal with sensing vibration?

1) Corpuscles of touch (helps detect lower frequency vibrations)
2) Lamelated pacinian corpuscles (helps detect higher frequency vibrations)
what were the five tactile somatic sensations?
Tickle, itch, vibration, pressure, touch
Time to talk about Itch and Tickle. Itch results from what?
Stimulation of *free nerve endings* by *certain chemicals* such as mosquito spit usually because of an inflammatory response.
What about tickle?
From *free nerve endings*
That was all Tactile. Now it’s time for thermal receptors. Describe them
Divided into warm and cool receptors.

Cold – Temps b/t 10 and 40 deg Celsius
Warm – Temps b/t 32 and 48 deg Celsius

Temps ABOVE 48 and BELOW 10 activate the pain receptors

K, Time for pain receptors. What’s the other word for pain receptor?
Nociceptor (Picture yourself abusing your child and saying “NO YOU SHOULDNT HAVE TOUCHED THAT! BAD!!!”)
Where ARENT pain receptors located?
The brain
What are the two TYPES of pain?
Fast and Slow

Fast: Stabbing myself with a needle
Slow: Chronis, burning, throbbing, DEEP or INTERNAL (toothache)

Pain can also be classified as either…?
Superficial somatic – skin
, deep somatic – muscles, joints, tendons
and Visceral – visceral organ pain
Define: Reffered pain
Feeling pain on the skin above the organ that’s in pain
Okay, so we’ve done tactile, thermal, pain, and now we move onto the last one…?
Proprioceptive
What does proprioceptive do?
Allows us to know where our head and free limbs are and how they’re moving even if we arent looking at them
Define: Kinesthesia
Perception of *body movements*
Define: Proprioceptors
The receptors that propripceptive sensations arise in
Talk about proprioceptors that exist in muscles
They let us know to what degree our muscles are contracted
What are the four types of proprioceptors?
1) Muscles spindles – In skeletal muiscles
2) Tendon organs – In tendons
3) Joint kinesthetic receptoes – located within synovial joint capsules
4) Hair cells – inner ear
Explain adaption and proprioceptors
They adapt SLOWLY and only SLIGHTLY…so the brain constantly receives nerve impulses related to the positionof different body parts………if we had good adaption here we’;d be screwed, that would mean that if we sat in a position for too long and moved it would take awhile to feel like we moved
Proprioceptive nerve impulses pass along (ascending/descending) tracts in the spinal cord to the _______ and from there to the _________ area of the ________ ________
`Ascending; thalamus; somatosensory; cerebral cortex
Where do prioprioceptive impulses ALSO pass along? Why do they go here too?
Spinocerebellar tracts to the cerebellum; they go here in ordrr to *coordinate muscle contractions*…coordinate is the key word…they’re send mainly to the somatic sensory area just to let us know where they’re at in space (our muscles)
What are the four types of proprioceptors?
1) Muscles spindles – In skeletal muiscles
2) Tendon organs – In tendons
3) Joint kinesthetic receptors – located within synovial joint capsules
4) Hair cells – inner ear
Muscles spindles are the proprioreceptors in skeletal muscles that monitor changes in the ______ of skeletal muscles and participate in stretch reflexes.
By adjusting how vigorously a muscle spindle responds to stretching of a skeletal muscle, the brain sets an overall level of _______ ______, which is the small degree of contraction that is present while the muscle is at rest
length ;muscle tone
A muscle spindle consists of # to ## specialized muscle fibers called __________ _______ _______
3 to 10 specialized muscle fibers called *intrafusal muscle fibers*

So these intrafusal muscle fibers are what the neurons in the muscle attaches to

What surrounds a muscle spindle?
Extrafusal muscle fibers
The central area of the intrafusal fiber is innvercated [supplied] by two types of afferent (away) fibers that do what?
Detect stretching (look at diagram on page 703)
The main function of muscle spingles is to measure muscle __________,
Muscle length – so how much the muscle is being stretched
Both ends of an intrafusal fiber contain actin and myosin filaments and contract when stimulated by what?
Gamma motor neurons – these ar ebasically the spindles own stretching thingy’s so that it can do its job of detecting the main muscles contractions without being affected by it
In addition to gamma motor neurons, we also have alpha motor neurons. What are alpha motor neurons?
THey innervate the extrafusal muscles to contract
Muscle spindles monitor changes in the length of skeletal muscles in order to prevent overstretching of the muscles; this info is relayed to the _____ _____ to provide perception of lumb position and is also relayed to the ________ to aid in muscle contraction coordination
Cerebral cortex; cerebellum
God that took forever, time for the next proprioreceptor, *Tendon organs*. Tendon organs are located at the junction of a tendon and a _______
muscle
What do tendon organs do?
Detect *tension* applied to a tendon
The last proprioceptive type is Joint Kinesthetic receptors…..there are several types of joint kintesthetic receptors located within and around the ______ ________ of _______ ________
articular capsules of synovial joints
Describe what types of nerves and receptors and any other crap is involved with joint kinesthetic receptors and explain them.
1) Free nerve endings and Type II mechano receptors in joint capsules to detect *pressure*
2) Lamellated corpuscles *outside* articular capsules detect the *acceleration* and *deceleration* of joint movement
Receptors (simuliar to tendon organs) in articular ligaments adjust adjacent muscles when _____ _______ is placed on a joint
Excessive pain
Now we move onto a nother topic, SOmatic sensory *pathways*. What do they do?
Relay info from somatic receptors to the primary somatosensory areas in the cerebral cortex and to the cerebellum
The pathways to the cerebral cortex consist of thousands of sets of THREE neurons….which are…?
First, second, and third-order neurons
What does first order neurons carry?
Carry Signals *from* somatic receptors into the brain stem or spinal cord via *cranial nerves* or *spinal nerves*
Second order?
Carry signals *from* the spinal cord and brain stem to the *thalamus*
What’s special about axons involved in second order?
They *decussate* , or cross to the opposite side before ascending to the thalamus…thus, all somatic sensory info from one side of the body reaches the thalamus on the opposite side
Third order?
Project from the thalamus to the primary somatosensory areas where conscious perception of sensations reulsts
There are TWO general pathways by which somatic sensory signals entering the spinal cord ascend to the cerebral cortex…what are they?
1) Posterior column-medial meniscus pathways
2) Anterolateral pathways
1) Posterior column-medial meniscus pathways transmit wwhat two types of nerve impulses usually/=?
COnscious proprioception and tactile sensation
Axons of the first order neurons form the __________ ________ ______ within the posterior column-medial lemniscus pathway
Posterior columns….they at bottom
The PD columns are made up what two things?
Gracile and Cuneate fasiculus
Axons of second order class will decussate in the _________ and enter the _______ ________, which is a projection tract that extends fron =the medulla to the thalamus
medulla; medial lemnisccus connect medulla and medial lemniscus
Axons of the third order project fromn the _______ to the -_______ __________ ________
Thalamus; primary somatosensory area
Impulses conducted along the posterior column-medial meniscus pathway give rise to what four sensations?
1) FIne touch
2) Proprioception and kinesthesia and Weight discrimination
3) steriogenisis – recognizing texture size shape etc
4) Vibratory sensations
There are TWO general pathways by which somatic sensory signals entering the spinal cord ascend to the cerebral cortex…what are they?
1) Posterior column-medial meniscus pathways
2) Anterolateral pathways
Anterolateral pathways transmit nerve impulses for what?
Pain, temp, tickle, itch, crude touch, pressure, and vibrations
Axons of the first order anterolateral enter the spinal cord and synapse with….
second order neurons in the PD Gray horns
Axons of the second order neurons in the anterilateral pathway decussate and acsend to the brain stem in either one of two tracts….?
1) lateral spinothalamic tract – conveys impulses for pain and temp
2) anterior spinothalamic tract – converys impulses for tickle, itch, crude touch, pressure, and vibrations
Axons of the second order neurons of the anterolateral enter the thalamus and synapse with third order neurons which project to the primary __________ area
somatosensory.
Now there are also two other somatic sensory pathways we need to worry about, what are they and where do they carry info to?
1) Posterior Spinocerebellar tract
2) Anterior spinocerebellar tract

These are sent to the cerebellum, they are unconscious but are crucial for posture, balance and coordination type things

We are now moving on from somatic sensory pathways to somatic *motor* pathways…….both _______ and ________ motor pathways extend from the cerebral motor cortex to skeletal muscles
direct and indirect
Neural circuits in the brain and spinal cord orchestrate ALL voluntary and involuntary movements. All excitatoryu and inhibitory signals that control movement converge on the alpha motor neurons that extend out of the brain stem and spinal cord to supply skeletal muscles in the head and body. These neurons are also known as what?
*Lower motor neurons* (LMN’s)
LMNs have their cell bodies in the brain stem and _____ _______
spinal cord
Their axons extend from the motor nuclei of cranial nerves to what?
Skeletal muscles of the face and head and from the anterior gfray horns at all levels of the psinal cord to skeletal muscles of the limbs and trunks
ONLY lower motor neurons provide output from the CNS to _____ _______ _____
skeletal muscle fibers
It is for this reason that lower motor neurons are also referred to as the final common pathway. There are four groups of neurons that participate in control of movement by providing *input* to lower motor neurons. What are they?
1) Local circuit neurons
2) Upper motor neurons
3) Basal nuclei neurons
4) Cerebellar neurons
*Local circuit neurons*….?
Receive input from somatic sensory receptors and from higher centers in the brain. They are located close to lower motor neuron cell bodies and transmit their knowledge to lower motor neurons
The axons of *Upper motor neurons* descend into the ________, where most of the axons cross over and then they terminate in nuclei of ______ _______ or in the ______ _____ _______ of the spinal cord
Medulla (so they help with balance); cranial nerves; anterior gray horns of spinal cord
*Basal nuclei neurons* assist movement by providing input through the _________ to _______ _______ ________
Thalamus; upper motor neurons (UMN’s)
*Cerebellar neurons* also aid movewment by controlling the activity of_______ ________ ________ through the ________
upper motor neurons; thalamus
The above 4 groups of neurons participate in control of movement by providing input to ________ _________ __________
lower motor neurons
The ___________ _________ _______ is located in the precentral gyrus of the brain and is the major control region for the initiation of voluntary movements
Primary motor area
What other areas contribute fibers to the descending motor pathways?
The *premotor* area and the *primary somatosensory* area
The degree of representation of different muscles in the primary motor area is proportional to the what?
Number of motor units present in a particular muscle
The direct motor pathways convey impulses that result in *precise*, *voluntary* movements via three pairs of tracts containing axons of UMNs. What are the names of these three tract pairs?
1) Lateral corticospinal tracts
2) Anterior corticospinal tracts
3) Corticobulbar tracts
What’s another name for direct motor pathways?
Pyramidal pathways
Describe the bolded:

*1) Lateral corticospinal tracts*
2) Anterior corticospinal tracts
3) Corticobulbar tracts

*1) Lateral corticospinal tracts*
-Most of the axons of the UMN’s decussate in the MEDULLA to form these in the RIGHT and LEFT l>> WHITE columns of the spinal cord
-Axons of LMN’s exit all levels of the spinal cord to supply skeletal muscles in the *limbs*, *hands*, and *feet*

2) Anterior corticospinal tracts
3) Corticobulbar tracts

Describe the bolded:

1) Lateral corticospinal tracts
*2) Anterior corticospinal tracts*
3) Corticobulbar tracts

Describe the bolded:

1) Lateral corticospinal tracts
*2) Anterior corticospinal tracts*
-Axons of the UMN’s cross over in the medulla but descend on the SAME SIDE to form these tracts in the right and left >>> white columns.
-Axons of these LMNs exit the cervical and upper thoracic segements of the spinal cord to innervate muscles of the *neck* and part of the *trunk* thus coordinating movements of the *axial skeleton*
3) Corticobulbar tracts

Describe the bolded:

1) Lateral corticospinal tracts
2) Anterior corticospinal tracts
*3) Corticobulbar tracts*

Describe the bolded:

1) Lateral corticospinal tracts
2) Anterior corticospinal tracts
*3) Corticobulbar tracts*
-Some axons of UMNs extend to the midbrain where they form these in the right and left cerebral peduncles.
-THe axons terminate in nuclei of nine pairs of cranial nerves. LMNs of these cranial nerves convey nerve impuilses that control precise movement of EYES, tongue, NECK, chewing, FACIAL expression, and SPEECH

The indirect motor pathways, or extrapyramidal pathways, include all somatic motor tracts OTHER than the ____________ and ____________ tracts.
Corticospinal; corticobulbar
Indirect (extrapyramidal) motor output from the brain arises from various nuclei in the brain stem and travels along FIVE major pairs of spinal cord tracts and then terminates on _________ and ____
interneurons; LMN’s
What are those five major pairs of indirect spinal cord tracts?
1) Rubrospinal tract
2) Tectospinal tract
3) Vestibulospinal tract
4) Lateral reticulospinal tract
5) Medial reticulospinal tract
Describe each:

1) Rubrospinal tract
2) Tectospinal tract
3) Vestibulospinal tract
4) Lateral reticulospinal tract
5) Medial reticulospinal tract

1) Rubrospinal tract – Begins in red nuceleus and transmits nerve impulses to opposite side of body to regulate precise, discrete movements…especially in distal limbs

2) Tectospinal tract – Begins in colliculus and transmits nerve impulses to opp side of body to the neck muscles that control movements of the head in response to visual stimuli

3) Vestibulospinal tract – Begins in vestibuluar nucleus and transmits nerve impulses to *SAME* side of the body to regulate *muscle tone* in response to movements of the *head*; therefore it plays a major role in *balance*

4) Lateral reticulospinal tract- Begins in the reticular formation of the medulla; on the *same* side of the body
-Promotes FLEXOR
-Inhibites EXTENSOR
-DECREASES MUSCLE TONE

5) Medial reticulospinal tract – Begins in the pons; on the *same* side of the body.
-Inhibits FLEXOR
-Promotes EXTENSOR
-INCREASES MUSCLE TONE

Sensory input informs the CNS about changes in the internal and external environment.
No sh*t
Incoming sensory info is ________ with other sensory info within many regions of the CNS (i.e. Spinal cord, brain stem, cerebellum, basal ganglia, cerebral cortex)
integrated
As a result, any motor response to make a muscle contract or a gland secrete can be modified and responded to in any of these regions…motor portions of the cerebral cortex play a major role for doing what?
Initiating and controlling precise muscle movements
The basal ganglia largely integrate ________, _________ movements like walking
semivoluntary automatic movements
The cerebellum assists the motor cortex and basal ganglia by making body movements ________ and ________ and by contributing significantally to maintaining normal posture and balance
smooth; coordinated