Lecture 3: Neuroanatomy and physiology Flashcards
(35 cards)
What is the general motor pathway to induce a contraction?
A motor impulse arises from the Primary motor area neuron cells to execute a desired movement. The impulse travels down along the axon of the UPPER MOTOR neuron. The target destination is a muscle to induce a contraction.
Describe the pathway in more detail during the motor pathway.
the Axons converge from the cerebral hemisphere at the internal capsule and descend to the brainstem.
What is the internal capsule?
The internal capsule is a location of many converged fibers. An injury to the internal capsule would have a massive effect.
The axon in the brainstem carries the impulse to the
contralateral side of the body. Also called the pyramidal tract.
Describe the corticospinal tract
The pathway of the axon of the upper motor neuron of the cortex to the nerve cell of a spinal nerve
Describe the corticobulbar tract
The pathway of the axon of the upper motor neuron of the cortex to the nerve cell of a cranial nerve
What are some details about the corticospinal tract?
-The grey matter of the spinal cord is on the inside surrounded by white matter
- The grey matter assumes the shape of the letter H with Dorsal and Ventral Horns
- The axons descend lateral to the grey matter, their name is anatomically assigned :The lateral corticospinal tract.
The dorsal horn is
the relay center for sensory information, both Dorsal and ventral roots combine to form the nerve trunk
What are some more details of the dorsal horn
-The dorsal horn of the spine is the main relay site for sensory information
-There is a need for many synapses to transmit a variety of sensations
What is the ganglion?
- a structure that is used by the nervous system to provide a location for synapses.
- Due to the amount of synapses there is a need for more surface area to transmit neuron signals
What is an important fact about the Corticobulbar tract?
All the cell bodies of the lower motor neurons of cranial nerves receive bilateral corticobulbar input except , lower ½ of VII and all of XII, both receive contra-lateral input only
Cranial Nerve I
The olfactory nerve:
Olfactory receptor nerve cells { first order neuron} are in the nasal mucosa
Their axons go through Cribriform plate of ethmoid bone
They relay impulses to the olfactory bulb nerve cells { second order neuron} at the Orbitofrontal cortex.
The axons emerge from the olfactory bulb as the olfactory tract , and transmits impulses bilaterally to the Uncus
Damage could result in : Loss of smell or Olfactory hallucinations
Cranial Nerve II
The optic nerve : Vision
-The first order neuron cells for vision reception are those of the retina
The retina on the nasal side sees the lateral visual field { temporal}
fibers on the same side collectively form an optic nerve that travels through the optic canal to the cranial cavity
The second order neuron cell is at the Thalamus Lateral geniculate body
Cranial Nerve III
The Oculomotor nerve:
motor nucleus in the Midbrain , receives bilateral cerebral input
Reaches the orbit through the superior orbital fissure
Responsible for :
70 % of upper eyelid elevation
Movement of the eye ball in all directions except inward-downward, and lateral
Has an autonomic effect
Describe Autonomic function of the Oculomotor nerve
an autonomic effect : ciliary muscle for the lens of the eye { accommodation} , and constrictor papillae , the autonomic fibers are superficial to the motor fibers on the nerve trunk .
If the lesion is external compression the autonomic function is lost , if the lesion is loss of intraneural blood supply , the motor function is lost
Testing for motor function: Ask the patient to move the eye in all directions .
Testing for autonomic function : Shine a torch light into one eye , there should be a pupillary constriction on both sides . This implies that the sensory input is resulting in simultaneous motor nucleus stimulation.
Cranial Nerve IV
The trochlear
Purely motor , motor nucleus in Midbrain , supplies muscle responsible for inward- downward eye movement . Receives bilateral cerebral Input. Reaches the orbit through the superior orbital fissure
Cranial Nerve VI
The Abducent
Purely motor , motor nucleus in Pons , supplies muscle responsible for lateral eye movement. Receives bilateral cerebral Input. Reaches the orbit through the superior orbital fissure.
Testing for movement and , asking about diplopia ;
Double vision of the same object.
Input from both eyes no longer synchronized
Cranial Nerve V
Trigeminal
Motor and Sensory. Motor nucleus in Pons . Three Divisions. Bilateral cerebral motor input.
{Ophthalmic, Maxillary, Mandibular }
Describe the sensory portion of the Trigeminal Nerve
Sensory: All the face except angle of mandible , general sensation from anterior 2/3 of the tongue & the buccal cavity
First order neurons : The nerve cells of those neurons are bipolar and are located in the trigeminal ganglion {two long axonal processes} .
The peripheral axons collect the sensations from the periphery
Explain how the fibers of the Trigeminal enter the Cranium
The Ophthalmic fibers enter the Cranium through the superior orbital fissure of the sphenoid bone
The Maxillary fibers enter the Cranium through the Foramen Rotundum of the sphenoid bone
The Mandibular fibers enter the Cranium through Foramen Oval and foramen Spinosum
of the sphenoid bone,
Motor V
motor fibers arise from the Trigeminal nucleus in the pons receiving the upper motor neuron cortico-bulbar input from both hemispheres
The lower motor neuron fibers emerge from the Pons through the Trigeminal ganglion along the mandibular division and supply innervation to the muscles of mastication
Testing : Motor decline in masticatory power
Sensory loss of corneal reflex , ( see later)
Cranial Nerve VII
The facial Nerve
Motor, Sensory, & Autonomic
The Motor nucleus is in the Pons, The sensory nucleus is in the Medulla . It innervates the muscles of facial expression, Platysma, posterior belly of Digastric, Stapedius, Stylohyoid.
The upper half of the motor nucleus of the Facial nerve receives corticobulbar fibers from both cerebral hemispheres; the lower half of the motor nucleus receives corticobulbar fibers only from the contralateral side
The upper half of the nucleus supplies the upper half of the face , and the lower half of the nucleus supplies the lower half of the face
Sensory and Autonomic properties of Cranial Nerve VII
There is a Ganglion {Geniculate ganglion} within the facial canal. The nerve cell axon splits into 2 directions.
The peripheral branch is Sensory and Autonomic, it divides into two branches
1- The Greater Superficial petrosal. This relays in the Sphenopalatine ganglion before supplying autonomic fibers to the lacrimal gland
2- The Chorda Tympani exits from the Facial canal before the Stylomastoid Foramen , it supplies the submandibular and sublingual salivary glands. The fibers of the chorda tympani also act as first order neurons for taste for the anterior 2/ 3 of the tongue. The fibers relay in the solitary nucleus of the upper medulla
3- The second order neurons cross, and ascend to the Cortical sensory area of the other side
Describe the corneal reflex
When the surface of the eye ball is touched with a cotton or tissue gently, there is bilateral blinking
The afferent sensory information flows through the ophthalmic branch of trigeminal . The motor component is through the facial fibers exiting from the parotid gland to the muscles of facial expression
