Cranial NERVE Flashcards
How many Cranial Nerve Pairs underside of brain
12
How are Cranial Nerves Numbered?
With Roman numerals I to XII
About cranial nerves
Most are mixed both (sensory and motor) nerves
Some are primary sensory associated with special senses
Some are primarily motor innervate muscles or glad
Most are are attached to the brain stem :
First pair- CN I has fibers that start in the nasal cavity ( olfactory nerve)
Second pair- CN II ORIGINATED IN EYES ( Optic nerve)
Oculomotor Nerves
Primary function
Motor (eye movements)
Somatic Motor
* Superior, Inferior and medial rectus muscles
* Inferior Oblique
* Levator palpebrae Superioris
Visceral Motor
* Intrinsic eye muscles (ciliary ganglion)
*Ciliary ganglion nerouns control intrinsic eye muscle ( pupil dilation or contraction)
Deliver autonomic fibers to neurons of ciliary ganglion
Trochlear Nerves
Primary Function:
*Motor ( eye movement)
Destination
*Superior Oblique
Abducens Nerves ( VI)
Primary Function
*Motor (eye movements)
Destination
*Lateral Rectus
Vestibulocochlear Nerve ( VIII)
Also called acoustic or auditory nerve
* Sensory Nerve only
2 branches includes
*Vestibular branch :Sensory from equilibrium receptors of ear
*Cochlear branch: Sensory from hearing receptors
Glossopharyngeal Nerve ( IX)
Mixed Nerve
Sensory from Pharynx, tonsils, part of tongue ( The region posterior to the nasal Cavity, oral cavity and larynx)
Motor impulses to salivary glands and muscles of pharynx for swallowing
Accessory Nerve (XI)
Primarily motor nerve
Formerly called “Spinal Accessory”
Contains cranial and spinal branches:
*Cranial branch : Joins Vagus N; Motor impulses to muscles of soft palate, pharynx and larynx
*Spinal Branch: Motor to muscles of neck and back ; small sensory component ( proprioceptivr fibers)
Hypoglossal Nerve (XII)
Primarily motor nerve
Motor impulses to muscles of the tongue for speaking, chewing, swallowing
- Small sensory component ( Proprioceptive fibers)
3 types of muscle tissue in the muscular system
Skeletal Muscle
Cardiac Muscle
Smooth Muscle
About skeletal Muscle
Attached to bones of skeleton
Voluntary ( consciously controlled)
Multi- Nucleate( multiple nuclei per cell)
Striated (actin - myosin interaction in sarcomere)
About Cardiac Muscle
Makes up most of the wall of heart
Involuntary (non consciously controlled)
Single nucleus (one nucleus per cell
Striated ( Actin-myosin interactions in sarcomere)
Responsible for pumping action of heart
About smooth muscles
Found in walls of internal organs , such as those of digestive tract
Involuntary ( non-consciously controlled)
Single nucleus ( one nucleus per cell)
Non-striated ( no well developed sarcomere)
More about skeletal Muscles
Over 600 skeletal muscles in the body
Under conscious control (Voluntary)
Attached to bones and skin over face
Are organs of the muscular system
Skeletal muscles are composed of
Skeletal muscle tissue
Nervous tissue
Blood
Connective tissue
About connective tissue of muscle
Connective tissue coverings over skeletal muscles!
*Fascia-thin covering of connective tissue around a muscle
Tendon- Cord-like mass of connective tissue that connects muscle to bone
Aponeurosis-Sheet like mass of connective tissue that connects a muscle to bone , skin, or another muscle
Connective tissue in and closely surrounding a muscle
Epimysium: Surrounds whole muscle;lies beneath fascia
Perimysium: Surrounds fascicles within a muscle
Endomysium: Surrounds muscle fibers (cells) with a fascicle
About Skeletal Muscle Fibers
Multinucleated
Sarcolemma: Cell Membrane of muscle fiber
Sarcoplasm: Cytoplasm of muscle fiber
Many myofibrils:
Long , parallel structures that run down
Consists of thin actin filaments and thick myosin filaments
Sarcomeres:Units that connect end to end , to make up myofibrils
More about Skeletal Muscles Fibers
- Sarcoplasmic Reticulum (SR) : Endoplasmic reticulum of muscle;stores calcium
*Transverse ( T) Tubule : Relays electrical impulses to the SR
*Triad: Unit consisting of 1 tubule and SR cisternae
Skeletal Muscle Fiber Structure
Myofibrils consists of sarcomeres connected end to end.
Striation pattern is made by arrangement of myofilaments in myofibrils
A sarcomere consists of these structures
I band: Light band, composed of thin actin filaments.
A band: Dark band ; composed of thick myosin filaments with portions overlapped with thin actin filaments.
H zone: Center of A band; composed of thick myosin filaments
Z line ( Z disc); Sarcomere boundary; in center of I band anchors filaments in place
M line : Center of sarcomere and A band ; anchors thick filaments
Thin and Thick Filaments in muscle fibers
Thick filaments:
Composed of myosin protein
Heads form cross-bridges with thin filaments
Thin filaments
*Composed of actin protein
* Associated with troponin and tropomyosin . Which prevent cross bridge forms when muscles is not contracting
Skeletal Muscle contraction
Requires interaction from several chemical and cellular components.
Results from a movement within the myofibrils, in which the actin and myosin filaments slide past each other, shortening the sarcomeres
Muscle fiber shortens and pulls on attachment points.
Neuromuscular Juno ( NMJ)
*A type of synapse
*Site where an axon of motor neuron and skeletal muscle fiber interact.
*Skeletal muscle fibers only contract when stimulated by a motor neuron
Parts of a Neuromuscular Junction
Motor Neuron : Neuron that controls skeletal muscle fiber.
Motor end plate: Specialized folded portion of skeletal muscle fiber ,where fiber binds to neurotransmitter
Synaptic Cleft: Space between neuron and muscle fiber, across which neurotransmitter travels.
Synaptic Vesicles : Membrane bound sacs containing neurotransmitter
Neurotransmitters: Chemicals released by motor neuron to deliver message to muscle fiber.
Neuromuscular Junction Excitation
Acetylcholine ( ACh) is the neurotransmitter.
Nerve impulse ( action potentials) causes release of ACh from synaptic vesicles in the motor neuron.
ACh binds to ACh receptors on motor end plate.
ACh causes changes in membrane permeability to sodium and potassium ions, which generates a muscle impulse(action potential)
- Impulse cause release of calcium ion from sarcoplasmic reticulum, which leads to muscle contractions
Myasthenia Gravis (MG)
An autoimmune disorder
Antibodies attack acetylcholine
receptors on skeletal muscle fibers ( motor end plates) in neuromuscular junctions.
Persons may have only one third normal number of ACh receptors
Leads to widespread muscle weakness and muscle fatigue
Treatments:
Drugs that inhibit acetylcholinesterase (an enzyme that breaks down acetylcholine and removes it from acetylcholine receptors)
Immunosuppressants drugs
Administering antibiotics that inactivate harmful antibodies
Plasma exchange
Muscular dystrophy
Deficiency or abnormality/mutation in scarce muscle protein called dystrophin
Binds to internal side of muscle cell membranes, and holds them together during concentration
In absence of normal dystrophin , cell lose normal structure and die
Clostridium Botulinum
Anaerobic bacteria that produce a toxin that prevents the release of ACh from the pre-synaptic neuron at the neuromuscular junction.
Grows in food that is not properly preserved
If ACh is not released from the neuron at the NMJ, what symptoms will occur?
Digestive, muscular, respiratory symptoms
Treated with an antitoxin
Used in small doses as Botox to smooth wrinkles, treat migraines
Excitation-contraction Coupling
Connection between muscle fiber stimulation and muscle contraction.
During muscle relaxation
Ca+2 ions are stored in SR
Troponin tropomyosin complex’s cover binding sites on actin filaments
Upon muscle stimulation
Action potentials cause SR to release Ca +2 ions into cytosol
Ca+2 ion bonds to troponin to change its shape
Each tropomyosin is held in place by a troponin molecule; change in shape of troponin alters the position of tropomyosin, exposing the binding sites on actin
Myosin heads bind to actin, forming cross bridges
Sliding Filament Model of Muscle contraction
When sarcomeres shorten , thick and thin filaments slide past each other
H zones and I bands narrow
Z lines move closer together
Thin and thick filaments do not change length
Overlap between filaments increases
Order of events in Cross-Bridge Cycling
1) Myosin head attaches to actin binding site , forming cross bridge
2)Myosin cross bridge pulls thin filament toward center of sarcomere
3). ADP and phosphate are released from myosin
4)New ATP binds to Myosin
5). Linkage between actin and myosin cross bridge break
6) ATP splits
7). Myosin cross bridge goes back to original postion , ready to bind to another binding site actin
Relaxation of muscles
When neural stimulation of muscle fiber stops:
Acetylcholinesterase enzyme rapidly decomposes ACH remaining in the synapse
Muscle impulse stops when ACh is decomposed
Stimulus to sarcolemma and muscle fiber membrane ceases
Calcium pump ( requires ATP) moves
Ca+2back into sarcoplasmic reticulum (SR)
Troponin tropomyosin complex again covers binding sites on actin
Myosin and actin binding are now prevented
Muscle fiber relaxes
ATP reserves
First source of energy for muscle contraction
Muscle cells store only a small amount
Creatine Phosphate
Initial source of energy to regenerate ATP from ADP and P
Stores energy in phosphate bond like ATP
ATP + creatine phosphate can only fuel 10 seconds of intense muscle contraction
Cellular respiration
Must be used to fuel longer periods of muscle contraction
Breaks down glucose to produce ATP
Glucose stored as glycogen in muscle cells
