Frog Nervous System

Questions for research:
1. Organs in the major divisions of the nervous system….
2. Functions of the nervous system….

a. Neurons and synapses
Most neurons send signals via their axons, although some types are capable of dendrite-to-dendrite communication. (In fact, the types of neurons called amacrine cells have no axons, and communicate only via their dendrites.) Neural signals propagate along an axon in the form of electrochemical waves called action potentials, which produce cell-to-cell signals at points where axon terminals make synaptic contact with other cells. b. Neural circuits and systems

The basic neuronal function of sending signals to other cells includes a capability for neurons to exchange signals with each other. Networks formed by interconnected groups of neurons are capable of a wide variety of functions, including feature detection, pattern generation, and timing. c. Reflexes and other stimulus-response circuits

The simplest type of neural circuit is a reflex arc, which begins with a sensory input and ends with a motor output, passing through a sequence of neurons in between.[51] For example, consider the “withdrawal reflex” causing the hand to jerk back after a hot stove is touched. The circuit begins with sensory receptors in the skin that are activated by harmful levels of heat: a special type of molecular structure embedded in the membrane causes heat to change the electrical field across the membrane. If the change in electrical potential is large enough, it evokes an action potential, which is transmitted along the axon of the receptor cell, into the spinal cord. There the axon makes excitatory synaptic contacts with other cells, some of which project (send axonal output) to the same region of the spinal cord, others projecting into the brain. 3. Cranial and spinal nerves…

Cranial nerve| Origin| Innervation|
Olfactory| Telencephalon| Transmits the sense of smell from the nasal cavity.[1] Located in olfactory foramina in thecribriform plate of ethmoid.| Optic| Diencephalon| Transmits visual signals from the retina of the eye to the brain.[3] Located in the optic canal.| Oculomotor| Anterior aspect of Midbrain| Innervates the levator palpebrae superioris, superior rectus, medial rectus, inferior rectus, andinferior oblique, which collectively perform most eye movements. Also innervates the sphincter pupillae and the muscles of the ciliary body. Located in the superior orbital fissure.| Trochlear| Dorsal aspect of Midbrain| Innervates the superior oblique muscle, which depresses, rotates laterally, and intorts the eyeball. Located in the superior orbital fissure.| Trigeminal| Pons| Receives sensation from the face and innervates the muscles of mastication. Located in thesuperior orbital fissure (ophthalmic nerve – V1), foramen rotundum (maxillary nerve – V2), andforamen ovale (mandibular nerve – V3).| Abducens| Nuclei lying under the floor of the fourth ventricle Pons| Innervates the lateral rectus, which abducts the eye. Located in the superior orbital fissure.|

Facial| Pons(cerebellopontine angle) above olive| Provides motor innervation to the muscles of facial expression, posterior belly of the digastric muscle, and stapedius muscle. Also receives the special sense of taste from the anterior 2/3 of the tongue and provides secretomotor innervation to the salivary glands (except parotid) and thelacrimal gland. Located in and runs through the internal acoustic canal to the facial canal and exits at the stylomastoid foramen.| Acoustic or Vestibulocochlear(or auditory-vestibular nerveor acoustic nerve| Lateral to CN VII (cerebellopontine angle)| Senses sound, rotation, and gravity (essential for balance and movement). More specifically, the vestibular branch carries impulses for equilibrium and the cochlear branch carries impulses for hearing. Located in the internal acoustic canal.| Glossopharyngeal| Medulla| Receives taste from the posterior 1/3 of the tongue, provides secretomotor innervation to theparotid gland, and provides motor innervation to the stylopharyngeus. Some sensation is also relayed to the brain from the palatine tonsils. Located in the jugular foramen.

Vagus| Posterolateral sulcus ofMedulla Supplies branchiomotor innervation to most laryngeal and pharyngeal muscles (except thestylopharyngeus, which is innervated by the glossopharyngeal). Also provides parasympatheticfibers to nearly all thoracic and abdominal viscera down to the splenic flexure. Receives the special sense of taste from the epiglottis. A major function: controls muscles for voice and resonance and the soft palate. Symptoms of damage: dysphagia (swallowing problems),velopharyngeal insufficiency. Located in the jugular foramen.| Accessory or spinal-acccessory(or cranial accessory nerveor spinal accessory nerve)| Cranial and Spinal Roots| Controls the sternocleidomastoid and trapezius muscles, and overlaps with functions of the vagus nerve (CN X). Symptoms of damage: inability to shrug, weak head movement. Located in thejugular foramen.| Hypoglossal| Medulla| Provides motor innervation to the muscles of the tongue (except for the palatoglossus, which is innervated by the vagus nerve) and other glossal muscles. Important for swallowing (bolus formation) and speech articulation. Located in the hypoglossal canal.|

Spinal Nerves:
We have 31 pairs of spinal nerves and they are named after the section of the spine they come out of. * 8 pairs of cervical nerves (C1-C8)
* 12 pairs of thoracic nerves (T1 – T12)
* 5 pairs of lumbar nerves (L1-L5)
* 5 pairs of sacral nerves (S1-S5)
* 1 pair of coccygeal nerves (Co1)

Cervical Plexus
This plexus is located underneath the sternocleidomastoid muscle (from C1 – C4). Most of the branches innervate the skin of neck and deep neck muscles. The Phrenic nerve (C3, C4, C5) gets special mention that innervates the top of the diaphragm (after traveling down through thoracic cavity, along either side of the heart). Note that if both phrenic nerves are cut or if the spinal cord is severed above C3, breathing stops. The Brachial Plexus

This plexus gets contribution from the transitional area from neck into armpit (axilla) between C5 and T1. It provides almost all the innervation of the upper limb (this includes back and scapular muscles that control the limb). The organization of this plexus is also very messy. There’s mixing of branches and then a branching of branches and then mixing again. Note how there’s divisions, trunks and roots. Five nerves innervate the muscles of the arm:

1. Musculocutaneous innervates the biceps brachii and some overlying skin. (C5, C6, C7) 2. Median innervates anterior forearm muscles, some intrinsic hand muscles, and skin of lateral (anatomical position/toward thumb) palm. (C5, C6, C7, C8, T1) 3. Ulnar innervates intrinsic hand muscles and skin of the medial hand. (C8, T1) 4. Radial travels along radius and innervates Triceps brachii and muscles of the posterior compartment, and overlying skin. (C5, C6, C7, C8, T1) 5. Axillary innervates the deltoid and teres minor, and overlying skin. (C5, C6) The Lumbar Plexus

This plexus lies within the iliopsoas muscle and comes from between L1 and L4. The main branches innervate the anterior thigh. Smaller branches innervate some of the abdominal wall and iliopsoas muscle. Femoral nerve — innervates quadriceps femoris muscle and overlying skin Obturator nerve — innervates adductor muscles and overlying skin The Sacral Plexus

The sacral plexus lies caudal to the lumbar plexus (stems from L4 to S4) and is often referred together withthe lumbar plexus as the lumbosacral plexus. The branches innervate buttocks, pelvis, perineum and lower limb (except for anterior and medial thigh). Sciatic nerve, the largest nerve of the sacral plexus is actually two nerves wrapped in one sheath: Tibial nerve (L4,L5,S1,S2,S3) innervates posterior thigh, posterior leg (lower leg), and intrinsic muscles of foot Common fibular (peroneal) nerve (L4,L5,S1,S2) innervates muscles of the anterolateral leg (lower leg)

ACTIVITY #24

Ventral view
1-10 Cranial nerves
1 Olfactory I
2 Ophthalmic branch of trigeminal V
3 Pathetic IV
4 Optic II
5 Oculomotor III
6 Facial VII
7 Trigeminal V
8 Abducens VI
9 Facial VII and auditory VIII

10 Glossopharyngeal IX and vagus X
11-20 Spinal nerves
11 First
12 Second
13 Third
14 Fourth
15 Fifth
16 Sixth
17 Seventh
18 Eighth
19 Ninth

20 Tenth
21 Sciatic nerve
22 Filum terminale
23 Sympathetic nerve cord
24 Sympathetic ganglion
25 Ramus communicans
26 Spinal cord
27 Hypophysis
28 Infundibulum
29 Pituitary

30 Optic lobe
31 Optic chiasma
32 Cerebral hemisphere
33 Olfactory lobe
34 Eyeball

QUESTIONS FOR RESEARCH:
1. | CNS| PNS| ANS|
a. Components| the brain and spinal cord| cranial and spinal nerves| sympathetic and parasympathetic chains of ganglia.| b. Location| Brain is contained in a bony structure known as brain box or cranium and protects it from the external shocks. Brain of frog consists of a pair of occipital condyles.| 10 pairs of cranial nerves are present and arise from the brain,10 pairs of spinal nerves that arise from the spinal cord emerge between the vertebrae and are located along the dorsal wall of body cavity| consists of two slender nerve trunks or cord, each with a chain of ganglia on either side of the spinal column | c. Distribution| Divided into five major parts, namely: Telencephalon Diencephalon Mesencephalon Metencephalon Myelencephalon| Cranial nerves extending from the lateral surfaces of the brain to the parts of the bodySpinal nerves distributes to the limbs and trunk.| operates through a series of interconnected neurons. frequently considered part of the peripheral nervous system (PNS), although many lie within the central nervous system(CNS).|

d. Function| Serves as the great center of communication between the principal sense organs and the rest of the body * Olfactory lobe of frog’s brain controls the sense of smell. * Optic lobes are invloved in the frog’s vision. * Cerebellum helps to maintain the balance and equilibrium of the frog. * Medulla oblongata helps in the regulation of respiration, digestion, and other automatic functions. Cerebellum also controls the muscular coordination and posture.| Cranial nerves are involved in passing the information from outside to the brain. Spinal nerves functions in passing information from the extremities to brain through spinal cord.| * helps deliver information to the body about impending danger * responsible for the fight-or-flight response |

2. Cranial nerves…
1. Olfactory
Origin: olfactory lobe
Location: walls of nasal chambers
2. Optic
Origin: optic chiasma.
Location: retina of the eyes
3. Oculo-Motor
Origin: arise dorsal to the lobes of the infundibulum
Location: 4 muscles of the eye namely (superior rectus,inferior rectus,medial rectus,inferior oblique muscles) 4. Trochlear
Origin: arises from the brain between the optic lobes and the cerebellum Location: superior oblique muscle of the eye

5. Trigeminal
Origin: arises from the medulla at its cephalo-lateral angle and passes into the prootic ganglion Location: muscles of the jaws, skin of the face, mouth and the tongue 6. Abducens
Origin: Close to the mid-line of the medulla
Location: lateral or external rectus muscle of the eye
7. Facial
Origin: Prootic ganglion palatine ramus
Location: muscles of the face and throat
8. Auditory
Origin: close behind the Vllth
Location: inner ear

9. Glossopharyngeal
Origin: arises from the sides of the medulla by four roots which it possesses in common with the tenth cranial nerve Location: floor of the mouth,tongue and pharynx
10. Vagus or Pneumogastric
Origin: arises from the sides of the medulla by four roots
Location: larynx,lungs,heart,esophagus,stomach and small intestine.