Anatomy & Physiology-II The Nervous SystemMr. Muhammad Nasir Khan, RMISoN

How Neurons Communicate at SynapsesFigure 7.10

The Reflex ArcReflex rapid, predictable, and involuntary responses to stimuliReflex arc direct route from a sensory neuron, to an interneuron, to an effectorFigure 7.11a

Simple Reflex ArcFigure 7.11b, c

Types of Reflexes and RegulationAutonomic reflexesSmooth muscle regulationHeart and blood pressure regulationRegulation of glandsDigestive system regulationSomatic reflexesActivation of skeletal muscles

Central Nervous System (CNS)Adult brain has 100 billion neurons.Weight of brain---1300 gLies in cranial cavity

Protection of the Central Nervous SystemScalp and skinSkull and vertebral columnMeningesFigure 7.16a

Protection of the Central Nervous SystemCerebrospinal fluidBlood brain barrierFigure 7.16a

MeningesThe brain and spinal cord are completely surrounded by 3 layers of tissue, The Meninges;Dura materDouble-layered external covering:Periosteum attached to surface of the skullMeningeal layer outer covering of the brain

MeningesArachnoid materMiddle layer CSF is present in the space below arachnoid mater (Sub arachnoid space)Pia materInternal layerAdheres to the surface of the brainPia mater & Arachnoid mater are collectively called Lepto meninges.

Cerebrospinal fluid (CSF)Fluid found in and around the central nervous system (CNS) organs, the brain and spinal cord.80- 90 % CSF is produced by ependymal cells within the lateral ventricles, remainder is produced by similar cells in third and fourth ventricles.These ependymal cells, their support tissue , and the associated blood vessels are called choroid plexuses.

Ventricles and Location of the Cerebrospinal FluidFigure 7.17a

Ventricles and Location of the Cerebrospinal FluidFigure 7.17b

CSF CompositionSecreted continuously at a rate of about 0.5ml per minute; 720ml per day. The volume remains fairly constant at about 150ml, as absorption keeps pace with the secretion.CSF pressure Normal 8 -10cm H2OAppearance; clear, colorlessWaterMineral saltsGlucose: 4085 mg/dL.Protein(total): 1545 mg/dL.Leukocytes(WBC): 05/L (adults / children)Specific gravity: 1.0051.009

CSF circulation:

Choroid plexus produces ~720ml/day of CSFbody produces, absorbs and replenishes the total volume of CSF about 3-4 times daily.)CSF produced in the lateral ventricles flows into the 3rd ventricle through an opening called interventricular foramenFlows into through a canal called cerebral aqueduct into the 4th ventriclePasses through paired lateral apertures and a median aperture into the subarachnoid space Flows through the subarachnoid space surrounding the brain (small amount enters the central canal of the SC)

Functions of CSF

Supports and protects the brain & spinal cord. Keeps the brain and spinal cord moist Supplies nutrients to the nervous system tissue. Removes waste products from cerebral metabolism.

Brain AnatomyThe Brain constitutes about one fiftieth of the body weight & lies within the cranial cavity.

Regions of the BrainCerebrum(Cerebral hemispheres)DiencephalonThalamusHypothalamusEpithalamus Brain stemMidbrainPonsMedulla OblangataCerebellumFigure 7.12

Cerebrum -The largest part of the brain. It is divided into two hemispheres, each of which is divided into four lobes.It is comprised of right and left hemispheres connected by the a band of white mater called as corpus callosum.The surface of the brain is convoluted to create more surface area.

Cerebral Cortex - The outermost layer of gray matter making up the superficial aspect of the cerebrum.

CEREBRAL FEATURESGyri or Convulsions Elevated ridges winding around of the brain.Sulci Small grooves dividing the gyri e.g. 1) Central Sulcus Divides the Frontal Lobe from the Parietal Lobe 2) Parietal-occipital sulcusFissures Deep grooves, generally dividing large regions/lobes of the brain 1) Longitudinal Fissure Divides the two Cerebral 2) Transverse Fissure Separates the Cerebrum from the Cerebellum3) Sylvian/Lateral Fissure Divides the Temporal Lobe from the Frontal and Parietal Lobes

Lobes of the CerebrumFissures (deep grooves) divide the cerebrum into 4 lobesLobes of the cerebrumFrontal lobeParietal lobeOccipital lobeTemporal lobe

Cerebral Lobes and their General FunctionsFrontal lobe. The top, front regions of each of the cerebral hemispheres used for reasoning, emotions, judgment, and voluntary motor movementParietal lobe. The middle lobe of each cerebral hemisphere between the frontal and occipital lobes; it contains important sensory centers.

Occipital lobe. The region at the back of each cerebral hemisphere that contains the centers of vision and reading ability (located at the back of the head). Temporal lobe. The region at the lower side of each cerebral hemisphere; contains centers of hearing and smell (located at the sides of the head).

Functional Areas of the CerebrumSensory areas receives impulses from the bodys sensory receptorsMotor areas sends impulses to skeletal musclesAssociation areas concerned with integration and processing of complex mental functions such as intelligence, memory, reasoning, judgement & emotions.

Functional Areas of Cerebral CortexMotor areas of Cerebral CortexPrimary motor area lies in the frontal lobe ant. To central sulcusBrocas area motor speech area, lies in frontal lobe above lateral sulcusSensory areas of Cerebral CortexThe somatosensory area lies immediately behind the central sulcus in the parietal lobe.The auditory area - Hearing area, lies in temporal lobeThe Olfactory area Smell area, lies deep within the temporal lobeThe Gustatory area Taste area, lies just above the lateral sulcusThe visual area lies in occipital lobeAssociation AreasThe Premotor area lies in frontal lobe anterior to motor areaThe prefrontal area - extend anteriorly from premotor area. Wernickes area Sensory speech, area lies in temporal lobe.

Sensory and Motor Areas of the Cerebral CortexFigure 7.14

Layers of the CerebrumGray matterOuter layerComposed of neuron cell bodiesFigure 7.13a

Layers of the CerebrumWhite matterMiddle part of the cerebrumComposed of nerve cell processes

Figure 7.13a

Layers of the CerebrumBasal GangliaGroups of cell bodies (nuclei) deep within the cerebral hemispheres.Act as a unified functional unit.Their functions include initiation and fine control of complex movement & learned coordinated activities such as posture and walking

Figure 7.13a

Functions of Cerebral CortexMental activities involved in memory, intelligence, sense of responsibility, thinking, reasoning, moral sense and learning.Sensory perception, including the perception of pain, touch, sight, hearing, taste & smell.Initiation and control of skeletal muscle contraction (voluntary movement)

Figure 7.13a