Motor Behavior Chapter 4

Types of Sensory receptors?

-Mechanoreceptors

-Thermoreceptors

-Nociceptors

-Photoreceptors

-Chemoreceptors

-Proprioceptors

What are Mechanoreceptors and where are they located?

-detect mechanical forces: touch, pressure, vibration, stretch

-Location: Skin, muscles, tendons, inner ear, blood vessels.

What are Thermoreceptors, and where are they located?

-detect temperature changes

-Location: Skin (dermis and epidermis), hypothalamus.

What are Nociceptors, and where are they located?

-pain receptors; detect harmful stimuli

-Location: Skin, muscles, joints, bones, most internal organs.

What are Photoreceptors, and where are they located?

-Detect light

-Location: Retina of the eye.

What are Chemoreceptors, and where are they located?

-detect chemical stimuli

-Location: Taste buds (tongue), Olfactory epithelium (nose), Carotid bodies & aortic bodies

What are Proprioceptors, and where are they located?

-Sense body position and movement

-Location: Muscles, tendons, joints, inner ear.

Describe a scenario that creates high sensory receptor acuity

-Reading Braille with your fingertips.

• The fingertips have many densely packed mechanoreceptors.

• Each receptor has a small receptive field, meaning it only responds to a tiny area of skin.

• When touching raised Braille dots, your brain can distinguish the location of each bump with high precision

Describe a scenario that creates low sensory receptor acuity

-Feeling a fly land on your back

• The skin on your back has fewer receptors spread out over a large area.

• Each receptor has a large receptive field, meaning it covers a bigger portion of skin

• Because of this, you might feel “something” touched your back but can’t pinpoint the exact location.

What is proprioception?

-The body’s ability to sense its position in spaces

-Tells you where your body parts are relative to each other and to the environment, even without looking.

-Receptors involved: Muscle spindles, Golgi tendon organs, joint receptors, vestibular apparatus (inner ear).

What is Kinesthesia?

-The body’s ability to sense the movement of muscles and joints

-Tells you how your limbs are moving, including direction, speed, and range of motion.

-Receptors involved: Same as proprioception, but with greater emphasis on muscle spindles and joint movement feedback.

Muscle Spindle is concerned with _____ while the GTO is concerned with ______?

-Muscle Spindle is concerned with muscle length and the rate of change in length (stretch).

-Golgi Tendon Organ (GTO) is concerned with muscle tension/force of contraction.

What are Intrafusal fibers?

-Specialized muscle fibers found inside the muscle spindle.

-Serve as sensory receptors that detect changes in muscle length and the rate of stretch. They do not generate significant force.

-Innervation:

• Sensory afferents (detect stretch)

• Gamma motor neurons (adjust spindle sensitivity)

What are Extrafusal fibers?

-The regular skeletal muscle fibers that make up most of the muscle.

-Responsible for generating force and movement.

-Innervation: Activated by alpha motor neurons.

Sensory afferents leaving the Muscle Spindle?

-Primary Afferents (Group Ia fibers)

-Secondary Afferents (Group II fibers)

What are Primary Afferents (Group Ia fibers)?

-Innervate: Wrap around the central region of both nuclear bag and nuclear chain intrafusal fibers.

-Function:

• Detect muscle length.

• Detect rate of change in length (velocity of stretch).

-Key Role: Super fast response → important in the stretch reflex (like the knee-jerk test).

What are Secondary Afferents (Group II fibers)?

-Innervate: Primarily the nuclear chain fibers (toward their ends).

-Function:

• Detect static muscle length (how stretched the muscle is at a given moment).

• Less sensitive to velocity.

What process allows the muscle spindle to continue to be effective in detecting and sending sensory information even when the muscle shortens during contraction?

-Alpha-Gamma Coactivation

What is the Alpha-Gamma Coactivation process?

-When a muscle contracts, the extrafusal fibers (force-producing fibers) shorten.

-If the intrafusal fibers inside the muscle spindle weren’t adjusted, they’d go slack and stop detecting stretch.

-To prevent this, gamma motor neurons stimulate the intrafusal fibers to contract at the same time as the extrafusal fibers.

-This keeps the muscle spindle taut and sensitive, so it can continue to detect changes in muscle length even during contraction.

What is AMI?

-Arthrogenic Muscle Inhibition

-Reflex inhibition of muscles surrounding a joint after injury (like swelling, pain, or inflammation).

-Mechanism:

• Joint receptors and afferents from swelling/pain send inhibitory signals to the spinal cord.

• This decreases excitability of alpha motor neurons to the affected muscle.

-Effect: The muscle (often the quadriceps after knee injury) can’t fully activate, even if you try voluntarily.

What is extensor thrust?

-Reflex extension of the limb when pressure is applied to the sole of the foot.

-Mechanism:

• Pressure stimulates cutaneous receptors

• Excites extensor motor neurons → causes the limb to straighten/extend.

What is a withdrawal reflex (flexor reflex)?

-Automatic flexion of a limb to pull away from a painful stimulus

-Mechanism:

• Nociceptors (pain receptors) are activated.

• Afferent fibers stimulate interneurons in the spinal cord.

• Excite flexor motor neurons → limb rapidly withdraws.

What is a crossed extensor reflex?

-Reflex that complements the withdrawal reflex to maintain balance.

-Mechanism:

• While one limb withdraws (flexes), the opposite limb reflexively extends to support body weight.

• Involves interneurons that cross the spinal cord midline

What does the Vestibular system do?

-body’s balance and spatial orientation system.

-tells your brain about head position, movement, and equilibrium, so you can stay upright, coordinate movement, and keep your vision stable.

-Gives you a sense of where you are in space (e.g., tilting, turning, or moving forward).

-Works with proprioception and vision to ensure smooth, coordinated body movements.

-Keeps your eyes focused on an object even when your head moves.

What is Righting?

-Righting is the set of reflexes that restore the normal alignment of the head, trunk, and limbs in relation to gravity and the environment.

-It’s primarily controlled by the vestibular system, visual input, and proprioception.

What are the structures of the eye?

-Cornea → clear front layer; bends (refracts) light most strongly.

-Aqueous Humor → fluid-filled space between cornea & lens.

-Lens → changes shape (accommodation) to fine-tune focus.

-Vitreous Humor → gel filling the eyeball, maintaining shape.

Anatomy of the Retina (sensory layer)

-Rods → dim-light (night) vision, black & white.

-Cones → color vision (red, green, blue sensitive), sharp detail.

-Macula lutea → central region with high cone density.

-Fovea centralis → sharpest vision, only cones.

-Optic disc (blind spot) → where optic nerve exits; no photoreceptors.

Parts of the central processing in the brain?

-Lateral Geniculate Nucleus (LGN) of the thalamus → relay station.

-Primary Visual Cortex (V1, occipital lobe) → first cortical processing of vision.

-Higher Visual Areas →

• Dorsal stream ("where pathway") → motion, spatial awareness.

• Ventral stream ("what pathway") → object recognition, color, detail.

What is the flow of vision?

-Light → Cornea → Pupil → Lens → Retina (rods/cones) → Optic Nerve → Optic Chiasm → Optic Tract → LGN (thalamus) → Visual Cortex → Higher Processing

What is Focal vision?

-Vision that uses the fovea (center of the retina) for sharp detail.

-requires head movement to center gaze and maintain sharpness

-conscious processing

-Identifies objects and details

What is Ambient vision?

-Uses both foveal detection and peripheral detection

-widespread subconscious processing

-Both dorsal and ventral streams

-detection of motion and relationships among objects

What is the Dorsal stream?

-Where/ how pathway

-Function:

• Processes spatial location, movement, and motion.

• Guides action and movement based on where objects are.

What is the ventral stream?

-What pathway

-Function:

• Processes object identity, color, shape, and detail.

• Recognizes faces, objects, and symbols.

What is Optic flow?

-The pattern of apparent motion of objects, surfaces, and edges in a visual scene caused by relative movement between an observer and the environment

-Function: Provides critical information about speed, direction, and distance during movement.

What is Tau?

-A variable that represents time-to-contact with an object based on visual information.

How does optic flow effect tau?

-As an object approaches, its image on the retina expands.

-The brain calculates tau from the rate of expansion in the optic flow, helping predict when the object will reach you.

-Example: Catching a ball – your brain estimates when it will reach your hand using optic flow and tau

How does optic flow effect motion perception?

-Optic flow provides continuous visual feedback about:

• Self-motion → how you’re moving through space.

• Object motion → how other objects move relative to you.

-Example: Driving on a road – the visual flow of the surroundings tells you speed and direction.

What is anticipation timing?

-The ability to coordinate a motor action to intercept or respond to a moving object.

How does optic flow effect anticipation timing?

-Helps the brain predict future positions of moving objects.

-Works with tau to time movements accurately.

-Example: Hitting a tennis ball – your brain uses the expansion of the ball’s image (optic flow) and tau to time your swing.