Spinal Cord & Special Senses Physiology

Ascending Tracts

Spinal cord pathways carrying sensory impulses up to the brain.

Descending Tracts

Spinal cord pathways carrying motor impulses down from the brain.

Reflex Arc Components

Sensory receptor/neuron, integrating center, motor neuron, and effector.

Stretch Reflex Mechanism

Muscle stretching activates muscle spindles, triggering motor neuron contraction.

General sens

includes somatic and visceral

Special senses

includes smell, taste, vision, hearing, equilibrium

Parts of PNS

cranial nerves, spinal nerves, ganglia, sensory receptors in skin, enteric plexuses in small intestine

Meissner Corpuscle

Encapsulated cutaneous receptor responsible for tactile sensation.

Pacinian Corpuscle

Encapsulated sensory receptor in skin detecting pressure and vibration.

Components of sensation

Stimulation of the sensory receptor

Signal Transduction (graded potentials)

Generation of nerve impulses

Integration of sensory input

Three Layers of the Eyeball Wall

Sclera/cornea (outer), choroid/iris/lens (middle), and retina (inner).

Pupillary Reflex in Dim Light

Sympathetic nervous system contracts radial muscles to dilate the pupil.

Pupillary Reflex in Bright Light

Parasympathetic nervous system contracts circular muscles to constrict the pupil.

Accommodation Reflex

Change in lens curvature via ciliary muscle contraction to focus near objects.

Cornea vs. Lens Refraction

Cornea provides fixed large refraction; lens provides variable refraction.

Lens Shape for Far Vision

Ciliary muscles relax, pulling suspensory ligaments to flatten the lens.

Lens Shape for Near Vision

Ciliary muscles contract, relaxing suspensory ligaments so the lens bulges.

Photopigment Composition

Consists of an opsin protein and a Vitamin A derivative (retinal).

Light Effect on Retinal (Isomerization)

Light changes retinal from cis-form to trans-form, separating it from opsin.

Rod Photoreceptors in Darkness

cGMP keeps Na+ channels open, depolarizing rods and releasing inhibitory glutamate.

Rod Photoreceptors in Light

cGMP converts to GMP, Na+ channels close, hyperpolarizing rods and disinhibiting bipolar cells.

Path of Signal Transduction in Retina

Photoreceptors → Bipolar cells → Ganglion cells → Optic nerve.

Rods vs. Cones Sensitivity & Acuity

Rods: high sensitivity, low acuity (night vision). Cones: low sensitivity, high acuity (color/day vision).

Primary Visual Cortex Location

Occipital lobe of the cerebral cortex.

Auditory Ossicles Order

Malleus → Incus → Stapes.

Organ of Corti Location

Housed within the cochlear duct of the inner ear.

Mechanism of Auditory Signal Transduction

Fluid vibrations move basilar membrane, bending hair cell stereocilia against tectorial membrane.

Pitch Perception on Basilar Membrane

High frequencies vibrate narrow/stiff base; low frequencies vibrate wider/flexible apex.

Tympanic membrane

It passes vibrations to the tiny bones (ossicles) in the middle ear from outter ear