The Central Nervous System

• The study notes cover the regions of the brain, protection for the brain, the spinal cord, spinal nerves, and the autonomic nervous system.

Regions and Organization of the CNS

• Brain regions include cerebral hemispheres, thalamus (diencephalon), brain stem (midbrain, pons, and medulla), and cerebellum.
• Spinal cord regions consist of gray and white matter that surrounds the central canal cavity with cerebrospinal fluid (CSF).

Gray and White Matter

• Gray matter mainly consists of networks of neuron cell bodies and unmyelinated fibers.
• White matter is composed of dense collections of myelinated fibers in the brain and spinal cord, primarily fiber tracts.

Cerebral Hemispheres – Surface Markings

• Ridges on the surface of the cerebral hemispheres are called gyri, and shallow grooves are called sulci.
• The five lobes of the cerebral hemispheres are the frontal, parietal, temporal, occipital, and insula.
• The central sulcus separates the precentral gyrus of the frontal lobe from the postcentral gyrus of the parietal lobe.
• The longitudinal fissure separates the two cerebral hemispheres.
• The transverse cerebral fissure separates the cerebrum and cerebellum.

Cerebral Cortex

• The cerebral cortex is the site of the conscious mind, enabling awareness, sensory perception, voluntary motor initiation, communication, memory, and understanding.
• The cortex is a thin (2-4 mm) superficial layer of gray matter.

Functional Areas of Cerebral Cortex

• Motor areas control voluntary movement.
• Sensory areas control conscious awareness of sensation.
• Association areas integrate diverse information.

Protection for the Brain

• The brain is protected by the bone (skull), membranes (meninges), a watery cushion of cerebrospinal fluid, and the blood-brain barrier.

Meninges

• The meninges cover and protect the CNS, protect blood vessels, and enclose venous sinuses.
• Cerebrospinal fluid (CSF) is contained within the meninges.
• The meninges form partitions in the skull.
• The three layers of meninges: dura mater, arachnoid mater, and pia mater.

Dura Mater

• The dura mater is the strongest layer of the meninges.
• The dura mater has two layers: periosteal and meningeal.
• The dura mater forms sinuses (venous blood) when the two layers separate.
• The Falx cerebri attaches the skull to the ethmoid bone in the longitudinal fissure.
• The Falx cerebelli is along the vermis of the cerebellum.
• The Tentorium cerebelli is a horizontal dural fold over the cerebellum and in the transverse fissure.

Arachnoid Mater

• The arachnoid mater is the middle layer of the meninges with weblike extensions.
• The subdural space separates the dura mater from the arachnoid mater.
• The subarachnoid space contains CSF and blood vessels and allows CSF to circulate around the CNS.
• Arachnoid villi protrude into the sinus and permit CSF reabsorption into venous blood.

Pia Mater

• The pia mater is a layer of delicate connective tissue that clings tightly to the brain.

Ventricles of the Brain

• Hollow chambers contain cerebrospinal fluid.
• Ventricles are connected to one another and to the central canal of the spinal cord.
• There are two C-shaped lateral ventricles in the cerebral hemispheres.
• The third ventricle is in the diencephalon (thalamus).
• The fourth ventricle is in the brainstem.

Cerebrospinal Fluid (CSF)

• CSF gives buoyancy to the CNS organs, protects the CNS from blows and other trauma, and nourishes the brain, carrying chemical signals.
• CSF is a watery solution that contains less protein and different ion concentrations than blood and plasma.
• CSF volume remains constant.

Choroid Plexuses

• Choroid plexuses produce CSF at a constant rate and hang from the roof of each ventricle.
• They consist of clusters of capillaries enclosed by pia mater and a layer of ependymal cells.
• Ependymal cells in the choroid plexuses use ion pumps to control the composition of the CSF and help cleanse it by removing wastes.

Blood-Brain Barrier

• The blood-brain barrier separates the CNS from the circulatory system and protects the brain from some blood-borne substances, helping maintain a stable environment.
• It consists of a continuous endothelium of capillary walls, a thick basal lamina externally surrounding the capillary, and the feet of astrocytes (neuroglia: support cells).
• CSF is absorbed into dural venous sinuses via arachnoid villi.

Spinal Cord

• It begins at the foramen magnum and ends as conus medullaris between the L1 and L2 vertebra.
• The spinal cord provides two-way communication to and from the brain and contains spinal reflex centers.

Spinal Cord Protection

• Spinal cord protection includes bone, meninges, and CSF.
• The epidural space, located between bony vertebrae and the dura mater, is filled with a cushion of fat and a network of veins.
• The spinal dura mater is a single layer, with the subdural space beneath.
• The arachnoid mater transitions to the subarachnoid space containing CSF, and then to the pia mater.
• The filum terminale is a fibrous extension from the conus medullaris that supports the spinal cord to the coccyx.

Spinal Cord Features

• The cervical and lumbar enlargements serve the upper and lower limbs.
• The ventral median fissure and dorsal median sulcus are two lengthwise grooves that divide the spinal cord into right and left halves.

White Matter of Spinal Cord

• White matter consists mostly of ascending (sensory) and descending (motor) tracts.
• Tracts are located in three white columns on either side: dorsal (posterior), lateral, and ventral (anterior) funiculi ('funiculus' single).

Gray Matter of Spinal Cord

• Dorsal horns receive somatic (body) and visceral (organ) sensory input.
• Ventral horns contain motor neurons whose axons exit the cord via ventral roots.
• Lateral horns are only in the thoracic and upper lumbar region and contain sympathetic neurons.

Spinal Nerves

• It has 31 pairs of nerves named according to their point of issue from the spinal cord.
• 8 cervical (C1–C8).
• 12 thoracic (T₁-T12).
• 5 Lumbar (L1-L5).
• 5 sacral (S₁-S5).
• 1 coccygeal (Co₁).
• Each spinal nerve connects to the spinal cord via dorsal and ventral roots.
• Dorsal roots contain sensory (afferent) fibers from sensory neurons and conduct impulses from the periphery towards the CNS.
• Ventral roots contain motor (efferent) fibers from the ventral horn motor neurons and conduct impulses from the CNS to the periphery.
• Dorsal and ventral roots merge to form spinal nerves that emerge from the vertebral column via intervertebral foramina.
• Each spinal nerve branches into dorsal and ventral rami.
• Dorsal rami innervate the back (sensory and motor).
• Ventral rami supply muscles of the ribs, abdominal wall, and skin.
• Remaining ventral rami form interlacing nerve networks called plexuses.

Ventral Ramus Form Plexuses

• Cervical Plexus -Formed by ventral rami of C1-C4 spinal nerves -Innervates skin and muscles of the neck, ear, back of the head, and shoulders

• Brachial Plexus -Formed by ventral rami of C5-C8 and T1 -Gives rise to the nerves that innervate the upper limb

• Major branches of brachial plexus -Five ventral rami (C5-T1) leads to upper, middle, and lower trunks leads to anterior and posterior divisions leads to lateral, medial, and posterior cords

Lumbar Plexus

• Arises from L1-L4.
• It mainly innervates the thigh, abdominal wall, and psoas muscles.
• The femoral nerve (deep to the inguinal ligament) innervates quadriceps and the skin of the anterior thigh and medial surface of the leg.
• The obturator nerve passes through the obturator foramen to innervate adductor muscles.

Sacral Plexus

• It arises from L4-S4.
• Serves the buttock, lower limb, pelvic structures, and perineum (inferior pelvis/genital structures).
• The Sciatic nerve is the longest and thickest nerve of the body and innervates the hamstring muscles, adductor magnus, and most muscles in the leg and foot.
• It composed to two of nerves: tibial and common fibular.
• The common fibular wraps around the head of the fibula, divides into deep and superficial fibular nerves.
• The tibial nerve serves in Dorsiflexion.
• The deep fibular supplies dorsi flexors of foot and the superficial fibular supplies fibularis group.

Autonomic Nervous System

• The central nervous system (CNS) is the brain and spinal cord integrates and commands the body.
• The peripheral nervous system (PNS) has paired spinal and cranial nerves.
• The autonomic nervous system (ANS) is sympathetic and parasympathetic and involuntary nervous system .

Autonomic Nervous System Divisions

• Sympathetic Nervous System (Flight or Fight). During activity mobilizes the body: ↑ adrenaline, ↑ BP, ↑ HR, ↑ respiration
• Parasympathetic Nervous System (Rest and Digest). Promotes maintenance activities and conserves body energy:↓ BP,↓ HR,↓ respiration,↑ gastrointestinal activity

Sympathetic Division (Thoracolumbar)

• Located cell body in lateral horn (ie only T1-L2).
• Axons in thoracic spinal nerves communicate with sympathetic chain.
• "Fight-or-Flight" mobilises the body during activity and promotes adjustments during normal activity or when threatened:↑ adrenaline, ↑ BP, ↑ HR,↑ respiration.

Parasympathetic Division (Craniosacral)

Cranial nerves- neuronal cell body in spinal cord, axon in the sacral spinal nerves -Promotes maintenance activities ↓ BP, ↓ HR, ↓Respiration, gastrointestinal activity