Central Nervous System: Brain Spinal cord

The Brain Performs the most complex neural functions Intelligence Consciousness Memory Sensory-motor integration Involved in innervation of the head

Organization of CNS Centrally located gray matter – neuron cell bodies, interneurons, unmyelinated fibers Externally located white matter – myelinated fibers Additional layer of gray matter external to white matter is the Cortex Formed from neuronal cell bodies migrating externally Located in cerebrum and cerebellum

Basic Parts and Organization of the Brain Divided into four regions Cerebral hemispheres - Account for 83% of brain mass Diencephalon – includes thalamus and hypothalamus Brain stem - includes midbrain, pons, and medulla Cerebellum – “little brain”

The Cerebral Hemispheres Frontal section through forebrain Cerebral cortex Cerebral white matter Deep gray matter of the cerebrum (basal ganglia) Corpus Callosum – commissural fibers (white matter) which connects the two hemispheres

The Cerebral Hemispheres Fissures – deep grooves, which separate major regions of the brain Transverse fissure – separates cerebrum and cerebellum Longitudinal fissure – separates cerebral hemispheres Sulci - grooves on the surface of the cerebral hemispheres Gyri - twisted ridges between sulci Prominent gyri and sulci are similar in all people

Lobes, sulci, and fissures of the cerebral hemispheres. Central sulcus Precentral gyrus Postcentral gyrus Frontal lobe Parietal lobe Parieto-occipital sulcus (on medial surface of hemisphere) Lateral sulcus Occipital lobe Temporal lobe Transverse cerebral fissure Cerebellum Pons (a) Medulla oblongata Spinal cord Gyrus Cortex (gray matter) Sulcus White matter Fissure (a deep sulcus)

The Cerebral Hemispheres Central sulcus separates frontal and parietal lobes Bordered by two gyri Precentral gyrus Postcentral gyrus Parieto-occipital sulcus - separates the occipital from the parietal lobe Lateral sulcus - separates temporal lobe from parietal and frontal lobes Deeper sulci divide cerebrum into lobes

The Cerebral Hemispheres Lobes are named for the skull bones overlying them Frontal Parietal Temporal Occipital

The Cerebral Cortex Home of our conscious mind Composed of gray matter - neuronal cell bodies, dendrites, and short axons Folds in cortex – triples its size Approximately 40% of brain’s mass

The Cerebral Cortex - Functional Areas Three general kinds of functional areas Sensory areas Association areas Motor areas Each of the major senses has a specific brain region called a primary sensory cortex There are also multimodal association areas to process information

Functional Areas Of The Cerebral Cortex Motor areas Central sulcus Sensory areas and related association areas Primary motor area Premotor cortex Primary somatosensory cortex 3 Frontal eye field 1 2 6 Somatic sensation 4 5 Somatosensory association area Broca’s area (outlined by dashes) 7 8 Gustatory cortex (in insula) Taste Prefrontal cortex Wernicke's area (outlined by dashes) Working memory for spatial tasks 45 43 44 22 Executive area for task management 41 42 19 18 22 17 Primary visual cortex Working memory for object-recall tasks 47 11 Visual association area Vision Solving complex, multitask problems Auditory association area Hearing Primary auditory cortex (a)

Primary Somatosensory Cortex Located along the postcentral gyrus Involved with conscious awareness of general somatic senses Motor areas Central sulcus Sensory areas and related association areas Primary motor area Premotor cortex Primary somatosensory cortex 3 1 2 Somatic sensation 4 5 Somatosensory association area 7 (a)

Primary Visual Cortex On medial part of the occipital lobe Largest of all sensory areas Receives visual information that originates on the retina First of a series of areas processing visual input 19 18 17 Primary visual cortex Visual association area Vision (a)

Primary Auditory Cortex Located at superior edge of the temporal lobe Conscious awareness of sound Impulses transmitted to primary auditory cortex Auditory association area Hearing Primary auditory cortex (a)

Olfactory Cortex Olfactory nerves transmit impulses to the olfactory cortex Provides conscious awareness of smells Lies on the medial aspect of the temporal lobe 18 18 Visual association area 34 17 28 Olfactory bulb Primary visual cortex Olfactory tract Temporal lobe (b) Fornix Primary olfactory cortex

Gustatory Cortex Involved in the conscious awareness of taste stimuli Located on the “roof” of the lateral sulcus Gustatory cortex (in insula) Taste (a)

Functional Areas Of The Cerebral Cortex Motor areas Central sulcus Sensory areas and related association areas Primary motor area Premotor cortex Primary somatosensory cortex 3 Frontal eye field 1 2 6 Somatic sensation 4 5 Somatosensory association area Broca’s area (outlined by dashes) 7 8 Gustatory cortex (in insula) Taste Prefrontal cortex Wernicke's area (outlined by dashes) Working memory for spatial tasks 45 43 44 22 Executive area for task management 41 42 19 18 22 17 Primary visual cortex Working memory for object-recall tasks 47 11 Visual association area Vision Solving complex, multitask problems Auditory association area Hearing Primary auditory cortex (a)

Motor Areas – Primary Motor Cortex Controls motor functions Located in precentral gyrus Motor areas Central sulcus Primary motor area Premotor cortex Primary somatosensory cortex 3 Frontal eye field 1 2 6 4 5 (a)

The Diencephalon Forms the center core of the forebrain, primarily composed of gray matter Surrounded by the cerebral hemispheres Composed of three paired structures: thalamus, hypothalamus, epithalamus Border the third ventricle

The Diencephalon Forms the center core of the forebrain, primarily composed of gray matter Surrounded by the cerebral hemispheres Composed of three paired structures: thalamus, hypothalamus, epithalamus Border the third ventricle Corpus callosum Septum pellucidum Fornix Interthalamic adhesion (intermediate mass of thalamus) Choroid plexus Thalamus (encloses third ventricle) Interventricular foramen Pineal body/gland (part of epithalamus) Corpora quadrigemina Hypothalamus Cerebral aqueduct Optic chiasma Pituitary gland Midbrain Arbor vitae Fourth ventricle Mammillary body Choroid plexus Pons Cerebellum Medulla oblongata Spinal cord

The Thalamus Makes up 80% of the diencephalon Contains approximately a dozen major nuclei Act as relay stations for incoming sensory message Every part of brain communicating with cerbral cortex relays signals through thalamic nuclei! Is the “gateway” to the cerebral cortex

The Hypothalamus Lies between the optic chiasm and the mammillary bodies Pituitary gland projects inferiorly Contains approximately a dozen nuclei Main visceral control center of the body The master gland’s master!!

The Diencephalon – The Hypothalamus Functions include the following Control of the ANS Control of emotional responses Regulation of body temperature Regulation of hunger and thirst sensations Control of behavior Regulation of sleep-wake cycles Control of the endocrine system Formation of memory

The Diencephalon – The Epithalamus Forms part of the “roof” (top) of the third ventricle Consists of a tiny group of nuclei Includes the pineal gland (pineal body) Secretes the hormone melatonin Under influence of the hypothalamus Aids in control of circadian rhythm

The Brain Stem Several general functions Produces automatic behaviors necessary for survival Passageway for all fiber tracts running between the cerebrum and spinal cord Heavily involved with the innervation of the face and head 10 of the 12 pairs of cranial nerves attach to it

The Brain Stem Includes the midbrain, pons, and medulla oblongata

The Brain Stem – The Midbrain The midbrain processes visual and auditory information and generates involuntary somatic motor responses Has reticular activing system-arousal of the whole brain Has nuclei for cranial nerves II and IV Has ascending and descending tracts

The Brain Stem – The Midbrain Lies between the diencephalon and the pons Cerebral peduncles located on the ventral surface of the brain, contain pyramidal (corticospinal) tracts Superior cerebellar peduncles - connect midbrain to the cerebellum

The Brain Stem – The Midbrain Corpora quadrigemina (quad-ri-gemina) The largest nuclei Divided into the superior and inferior colliculi Superior colliculi – nuclei that act in visual reflexes Inferior colliculi – nuclei that act in reflexive response to sound

The Brain Stem – Dorsal View Figure 13.13c

The Brain Stem – The Pons A “bridge” between the midbrain and medulla oblongata Pons contains the nuclei of cranial nerves V – Trigeminal nerve VI – Abducens nerve VII – Facial nerve Motor tracts coming from the cerebral cortex Pontine nuclei Connect portions of the cerebral cortex and cerebellum Send axons to cerebellum through the middle cerebellar peduncles

The Brain Stem – The Medulla Oblongata The core of the medulla contains Much of the reticular formation Nuclei then influence autonomic functions Cardiac center Vasomotor center The medullary respiratory center Centers for hiccupping, sneezing, swallowing, and coughing

Functional Brain Systems – The Reticular Formation Figure 13.29

The Brain Stem – The Medulla Oblongata Most caudal level of the brain stem Is continuous with the spinal cord Choroid plexus lies in the roof of the fourth ventricle Cranial nerves VIII–XII attach to the medulla External landmarks of medulla Pyramids of the medulla lie on its ventral surface Decussation of the pyramids - crossing over of motor tracts Inferior cerebellar peduncles - fiber tracts connecting medulla and cerebellum

The Cerebellum Located dorsal to the pons and medulla Smoothes and coordinates body movements Helps maintain equilibrium Consists of two cerebellar hemispheres Cortex – gray matter Arbor vitae - internal white matter Thick tracts connecting the cerebellum to the brain stem are superior, middle, inferior cerebellar peduncles

The Cerebellum Composed of Cortex – gray matter Arbor vitae - internal white matter Thick tracts connecting the cerebellum to the brain stem are Superior cerebellar peduncles Middle cerebellar peduncles Inferior cerebellar peduncles Fibers to and from the cerebellum are ipsilateral -run to and from the same side of the body

The Cerebellum Cerebellum receives information from the cerebral cortex On equilibrium On current movements of Limbs, neck, and trunk

Ventricles of the Brain Expansions of the brain’s central cavity Filled with cerebrospinal fluid Lined with ependymal cells Continuous with each other Continuous with the central canal of the spinal cord

Ventricles of the Brain Lateral ventricles – located in cerebral hemispheres Horseshoe-shaped from bending of the cerebral hemispheres Third ventricle – lies in diencephalon Connected with lateral ventricles by interventricular foramen Cerebral aqueduct – connects 3rd and 4th ventricles Fourth ventricle – lies in hindbrain Connects to the central canal of the spinal cord

Protection of the Brain The brain is protected from injury by The skull Meninges Cerebrospinal fluid Blood-brain barrier

Cerebrospinal Fluid (CSF) Formed in choroid plexuses in the brain ventricles Choroid plexus is Located in all four ventricles Composed of ependymal cells and capillaries Arises from blood - 500 ml/day

Cerebrospinal Fluid Fills the hollow cavities of the brain and spinal cord Provides a liquid cushion for the spinal cord and brain Other functions Nourishes brain and spinal cord Removes wastes Carries chemical signals between parts of the CNS

Cerebrospinal Fluid (CSF) Figure 13.32b

Blood Brain Barrier Extensive impermeable capillaries & sinuses Perivascular feet of astrocytes cover and wrap around capillaries and promote tight junction formation Protects brain from hormones & circulating chemicals Prevents most blood-borne toxins from entering the brain Not an absolute barrier Nutrients such as oxygen pass through Allows alcohol, nicotine, and anesthetics through Many glucose transporters Figure 9-6: The blood-brain barrier

Meninges Functions of meninges Cover and protect the CNS Enclose and protect the vessels that supply the CNS Contain the cerebrospinal fluid between pia and arachnoid maters

Meninges Dura Mater Arachnoid Mater Pia Mater Strongest of the meninges Composed of two layers: periosteal layer & meningeal layer Arachnoid Mater Located beneath the dura mater Arachnoid villi - Project through the dura mater, allow CSF to pass into the dural blood sinuses Pia Mater Delicate connective tissue, clings tightly to the surface of the brain Follows all convolutions of the cortex

The Spinal Cord Functions of the spinal cord Spinal nerves attach to it Provides two-way conduction pathway Major center for reflexes Location of the spinal cord Runs through the vertebral canal Extends from the foramen magnum to the level of the vertebra L1 or L2

The Spinal Cord Cervical and lumbar enlargements - where nerves for upper and lower limbs arise Conus medullaris - the inferior end of the spinal cord Cauda equina - collection of spinal nerve roots Filum terminale - long filament of connective tissue, attaches to the coccyx inferiorly

Spinal Cord Segments Indicate the region of the spinal cord from which spinal nerves emerge Designated by the spinal nerve that issues from it T1 is the region where the first thoracic nerve emerges

The Spinal Cord Two deep grooves run the length of the cord Posterior median sulcus Anterior median fissure

White Matter of the Spinal Cord White columns Dorsal (posterior) funiculus Ventral (anterior) funiculus Lateral funiculus Composed of myelinated axons Allow communication between spinal cord and brain

White Matter of the Spinal Cord Fibers classified by type Ascending fibers - afferent (sensory) Descending fibers – efferent (motor) Commisural fibers

Major Fiber Tracts in White Matter of the Spinal Cord Figure 13.34

Gray Matter of the Spinal Cord Shaped like the letter “H” Gray commissure – contains the central canal Dorsal horns consist of interneurons Ventral and lateral horns contain cell bodies of motor neurons

Organization of the Gray Matter of the Spinal Cord Divided according to somatic and visceral regions SS – somatic sensory VS – visceral sensory VM – visceral motor SM – somatic motor

Protection of the Spinal Cord Protected by vertebrae, meninges, and CSF Meninges Dura mater – a single layer surrounding spinal cord Arachnoid mater – lies deep to the dura mater Pia mater – innermost layer, delicate layer of connective tissue

Ascending Pathways Conduct general somatic sensory impulses Chains of neurons composed of First-, second-, and third-order neurons Four main ascending pathways Dorsal column pathway Spinothalamic pathway Posterior spinocerebellar pathway Anterior spinocerebellar pathway

Descending Pathways Most motor pathways Decussate at some point along their course Consist of a chain of two or three neurons Tracts arranged according to the body region they supply All pathways are paired - one of each on each side of the body Deliver motor instructions from the brain to the spinal cord Divided into two groups Pyramidal (corticospinal) tracts Other motor pathways Tectospinal tracts Vestibulospinal tract Rubrospinal tract Reticulospinal tract