Part 1.

Is a network of neurons whose main feature is to generate, modulate and transmit information between all the different parts of the human body.

Together with the endocrine system it controls important aspects of body function and maintains homeostasis.

Nervous system stimulation provides an immediate response while endocrine activity is, in the main, slower and more prolonged.

The nervous system is organized into two parts

The central nervous system

The peripheral nervous system

Consists of

The brain

The spinal cord

Both the brain and spinal cord are covered with a system of membranes, called meninges, and are suspended in the cerebrospinal fluid; and they are further protected by the bones of the skull and the vertebral column respectively.

Consisting of all the nerves outside the brain and spinal cord.

Classified into two systems

The somatic NS

The autonomic NS

Each system contains two components

The sensory (afferent) neurons: from receptors to the CNS

The motor (efferent) neurons: from CNS to the effector organ.

Responsible for voluntary, conscious control of skeletal muscles.

THE AUTONOMIC (VISCERAL) NS

Control the visceral functions of the body and acts largely unconsciously, involuntary.

Further subdivided into

The sympathetic nervous system

The parasympathetic nervous system

Is responsible for the fight or flight response of the body and originates from the thoracolumbar segments of the spinal cord.

The preganglionic neurons use acetylcholine as a neurotransmitter while the postganglionic neurons use noradrenaline.

The Parasympathetic NS

Is responsible for the rest and digest actions of the body, and it originates from craniosacral segments of the spinal cord.

Consists of long preganglionic neurons and short postganglionic neurons and both use the neurotransmitter acetylcholine.

Brain is a complex organ composed of nervous tissue that commands task-evoked responses, movement, senses, emotions, language, communication, thinking, and memory.

The brain is composed of three main structural divisions

The cerebrum

The brainstem

Midbrain

Pons

Medulla

The cerebellum

This is the largest part of the brain and it occupies the anterior and middle cranial fossae.

INTERNAL STRUCTURE

The cerebrum is comprised of two different types of tissue:-

Grey matter: forms the surface of each cerebral hemisphere and is associated with processing and cognition.

White matter: forms the bulk of the deeper parts of the brain. It consists of glial cells and myelinated axons that connect the various grey matter areas.

EXTERNAL STRUCTURE

Has a highly convoluted appearance, consisting of

Sulci: grooves or depressions

Gyri: ridges or elevations.

Divided into two hemisphere (left and right) by the longitudinal fissure – a major sulcus that runs in the median sagittal plane.

The falx cerebri ( a fold of dura mater) descends vertically to fill this fissure.

Corpus callosum, a white matter structure connect the two cerebral hemisphere.

LOBES OF THE CEREBRUM

Each lobe contains various cortical association areas – where information from different modalities are collated for processing.

Frontal lobe

Parietal lobe

Temporal lobe

Occipital lobe

Frontal lobe

Responsible for higher intellect, personality, mood, social conduct and language (dominant hemisphere only)

Parietal lobe

Contribute to the control of language and calculation on the dominant hemisphere side, and visuospatial functions ( eg 2- point discrimination) on non-dominant hemisphere side.

Temporal lobe

Accountable for memory and language – this includes hearing as it is he location of primary auditory cortex.

Occipital lobe

Responsible for vision as the primary visual cortex is located within the occipital lobe.

VASCULATURE

BLOODY SUPPLY

Anterior cerebral arteries

Middle cerebral arteries

Posterior cerebral arteries

VENOUS DRAINAGE

Via a network of small cerebral veins, emptying into the dural venous sinuses.

Midbrain

The rostral part of the brainstem

Pons

Is the part of the brainstem between the midbrain rostrally and the medulla oblongata caudally

Medulla oblongata (medulla)

Is the most caudal subdivision of the brainstem that is continuous with the spinal cord

Is the large brain mass lying posterior to the pons and medulla and inferior to the posterior part of the cerebrum.

It consists of two lateral hemispheres that are united by a narrow middle part, the vermis.

Functional Divisions

Cerebrocerebellum –It is involved in planning movements and motor learning. This area also regulates coordination of muscle activation and is important in visually guided movements.

Spinocerebellum –It is involved in regulating body movements by allowing for error correction.

Vestibulocerebellum – It is involved in controlling balance and ocular reflexes, mainly fixation on a target.

The meninges refer to the membranous covering of the brain and spinal cord.

They have two major functions

Provide a supportive framework for the cerebral and cranial vasculature.

Acting with cerebrospinal fluid to protect the CNS from mechanical damage.

Named from outside inward they are

The dura mater

Arachnoid mater

Pia mater.

The dura and arachnoid maters are separated by a potential space, the subdural space.

The arachnoid and pia maters are separated by the subarachnoid space, containing cerebrospinal fluid.

Some are sensory, some are motor and some are mixed

The CN I and CN II originate from the cerebrum.

CN III- XII arise from the brainstem.

Midbrain

Their names and numbers are

Olfactory: sensory

Optic: sensory

Oculomotor: motor

Trochlear: motor

Trigeminal: mixed

Abducent: motor

Facial: mixed

Vestibulocochlear (auditory): sensory

Glossopharyngeal: mixed

Vagus: mixed

Accessory: motor

Hypoglossal: motor.

Is the first and shortest cranial nerve

Origin: Olfactory epithelium of nasal cavity

Component: Sensory

Function: Smell from nasal mucosa of roof of each nasal cavity and superior sides of nasal septum and superior concha

Cranial Exit: Foramina in cribriform plate of ethmoid bone

Origin: Back of the eyeball

Component: Sensory

Function: Vision

Cranial Exit: Optic canal

The nerve passes posteromedially in the orbit, exiting through the optic canal to enter the middle cranial fossa, where it forms the optic chiasm. Here, fibers from the nasal (medial) half of each retina decussate in the chiasm and join uncrossed fibers from the temporal (lateral) half of the retina to form the optic tract.

Origin: Anterior surface of the midbrain

Component: Motor

Function

Raises upper eyelid

Turns eyeball upward, downward and medially

Constricts pupil

Accommodates the eye

Cranial Exit: Superior orbital fissure

Origin: Posterior surface of the midbrain

Component: Motor

Function: Assisting in turning eyeball downward and laterally

Cranial Exit: Superior orbital fissure

Has three main branches

V1: Ophthalmic Nerve

V2: Maxillary Nerve

V3: Mandibular Nerve

Origin: Anterior aspect of pons

Component: Sensory

Function

Cornea

Skin of forehead

Scalp

Eyelids and nose

Mucosa of nasal cavity and paranasal sinuses

Cranial Exit: Superior orbital fissure

Origin: Anterior aspect of the pons

Component: Sensory

Function

Skin of the face over maxilla, including upper lip

Teeth of the upper jaw (maxillary teeth)

Mucosa of nose, maxillary sinuses, and palate

Cranial Exit: Foramen rotundum

Origin: Anterior aspect of the pons

Component: Sensory and Motor

Function

Sensory: Sensation from skin and over side of head mandible including lower lip, mandibular teeth, temporomandibular joint, mucosa of mouth and anterior two thirds of tongue

Motor: Motor to muscles of mastication, mylohyoid, anterior belly of digastric, tensor veli palatini, and tensor tympani.

Cranial Exit: Foramen ovale

Origin: Pons

Component: Motor

Function: Motor to lateral rectus that turns eye laterally

Cranial Exit: Superior orbital fissure

Origin: Pons

Component: Sensory and Motor

Function

Motor

Motor to muscles of facial expression and scalp; also supplies stapedius of middle ear, stylohyoid, and posterior belly of digastric.

Secretomotor to submandibular and sublingual salivary glands, lacrimal gland, and glands of nose and palate

Sensory: Taste from anterior two thirds of tongue and the palate

Cranial Exit: Internal acoustic meatus; facial canal; stylomastoid foramen

Aka auditory/ acoustic nerve

Origin: Pons

Component: Sensory

Function

Vestibular: Vestibular sensation from semicircular ducts, utricle, and saccule related to position and movement of head

Cochlear: Hearing from spiral organ

Cranial Exit: Internal acoustic meatus

Origin: Medulla oblongata

Component: Sensory and Motor

Function

Motor

Motor to stylopharyngeus to assist with swallowing

Parasympathetic innervation to parotid gland

Sensory

Visceral sensation from parotid gland, carotid body and sinus, pharynx, and middle ear

Taste from posterior third of tongue

Cutaneous sensation from external ear

Cranial Exit: Jugular foramen

Origin: Medulla oblongata

Component: Sensory and motor

Function

Motor

Motor to constrictor muscles of pharynx (except stylopha-ryngeus), intrinsic muscles of larynx, muscles of palate (except tensor veli palatini), and striated muscle in superior two thirds of esophagus

Parasympathetic innervation to smooth muscle of trachea, bronchi, digestive tract, and cardiac muscle of heart

Sensory

Visceral sensation from base of tongue, pharynx, larynx, trachea, bronchi, heart, esophagus, stomach, and intestine to left colic flexure

Taste from epiglottis and palate

Sensation from auricle, external acoustic meatus, and dura mater of posterior cranial fossa

Cranial Exit: Jugular foramen

Origin: Medulla oblongata

Component: Motor

Function

Motor to sternocleidomastoid and trapezius

Motor to muscles of soft palate (except tensor veli palatini), pharynx (except stylopharyngeus), muscle of larynx (except cricothyroid)

Cranial Exit: Jugular foramen

Origin: Medulla oblongata

Component: Motor

Function: Motor to intrinsic and extrinsic muscles of tongue (except palatoglossus)

Cranial Exit: Hypoglossal canal

The spinal cord is the elongated, almost cylindrical part of the central nervous system, which is suspended in the vertebral canal surrounded by the meninges and cerebrospinal fluid.

It is continuous above with the medulla oblongata and extends from the upper border of the atlas to the lower border of the 1st lumbar vertebra.