Neuropsychology (Neuroanatomy)

Neuropsychology (Neuroanatomy)
Dr . Bakhshani NM Zahedan University of Medical Sciences Department of Clinical Psychology and Psychiatry

Structure of the Vertebrate Nervous System
Neuroanatomy is the anatomy of the nervous system. Refers to the study of the various parts of the nervous system and their respective function(s). The nervous system consists of many substructures, each comprised of many neurons.

Terms used to describe location when referring to the nervous system include: Ventral: toward the stomach Dorsal: toward the back Anterior: toward the front end Posterior: toward the back end Lateral: toward the side Medial: toward the midline

Figure 4.2: Terms for anatomical directions in the nervous system.
In four-legged animals, dorsal and ventral point in the same direction for the head as they do for the rest of the body. However, humans’ upright posture has tilted the head, so the dorsal and ventral directions of the head are not parallel to those of the spinal cord. Fig. 4-2, p. 83

The Nervous System is comprised of two major subsystems: The Central Nervous System (CNS) The Peripheral Nervous System (PNS)

Figure 4.1: The human nervous system.
Both the central nervous system and the peripheral nervous system have major subdivisions. The closeup of the brain shows the right hemisphere as seen from the midline.

The Central Nervous System consists of: Brain Spinal Chord

The spinal cord is the part of the CNS found within the spinal column and communicates with the sense organs and muscles below the level of the head. The Bell-Magendie law states the entering dorsal roots carry sensory information and the exiting ventral roots carry motor information. The cell bodies of the sensory neurons are located in clusters of neurons outside the spinal cord called dorsal root ganglia.

Figure 4.3: Diagram of a cross-section through the spinal cord.
The dorsal root on each side conveys sensory information to the spinal cord; the ventral root conveys motor commands to the muscles. Fig. 4-3, p. 84

The spinal cord is comprised of: grey matter-located in the center of the spinal cord and is denseley packed with cell bodies and dendrites white matter – composed mostly of myelinated axons that carries information from the gray matter to the brain or other areas of the spinal cord. Each segment sends sensory information to the brain and receives motor commands.

Spinal Cord Runs through the vertebral canal
Extends from foramen magnum to second lumbar vertebra Regions Cervical Thoracic Lumbar Sacral Coccygeal Gives rise to 31 pairs of spinal nerves All are mixed nerves Not uniform in diameter Cervical enlargement: supplies upper limbs Lumbar enlargement: supplies lower limbs Conus medullaris- tapered inferior end Ends between L1 and L2 Cauda equina - origin of spinal nerves extending inferiorly from conus medullaris. Spinal Cord

Meninges Connective tissue membranes Spaces
Dura mater: outermost layer; continuous with epineurium of the spinal nerves Arachnoid mater: thin and wispy Pia mater: bound tightly to surface Forms the filum terminale anchors spinal cord to coccyx Forms the denticulate ligaments that attach the spinal cord to the dura Spaces Epidural: external to the dura Anesthestics injected here Fat-fill Subdural space: serous fluid Subarachnoid: between pia and arachnoid Filled with CSF Meninges

Cross Section of Spinal Cord
Anterior median fissure and posterior median sulcus deep clefts partially separating left and right halves Gray matter: neuron cell bodies, dendrites, axons Divided into horns Posterior (dorsal) horn Anterior (ventral) horn Lateral horn White matter Myelinated axons Divided into three columns (funiculi) Ventral Dorsal lateral Each of these divided into sensory or motor tracts Cross Section of Spinal Cord

Cross section of Spinal Cord
Commissures: connections between left and right halves Gray with central canal in the center White Roots Spinal nerves arise as rootlets then combine to form dorsal and ventral roots Dorsal and ventral roots merge laterally and form the spinal nerve

Organization of Spinal Cord Gray Matter
Recall, it is divided into horns Dorsal, lateral (only in thoracic region), and ventral Dorsal half – sensory roots and ganglia Ventral half – motor roots Based on the type of neurons/cell bodies located in each horn, it is specialized further into 4 regions Somatic sensory (SS) - axons of somatic sensory neurons Visceral sensory (VS) - neurons of visceral sensory neur. Visceral motor (VM) - cell bodies of visceral motor neurons Somatic motor (SM) - cell bodies of somatic motor neurons

Gray Matter: Organization

White Matter in the Spinal Cord
Divided into three funiculi (columns) – posterior, lateral, and anterior Columns contain 3 different types of fibers (Ascend., Descend., Trans.) Fibers run in three directions Ascending fibers - compose the sensory tracts Descending fibers - compose the motor tracts Commissural (transverse) fibers - connect opposite sides of cord

White Matter Fiber Tract Generalizations
Pathways decussate (most) Most consist of a chain of two or three neurons Most exhibit somatotopy (precise spatial relationships) All pathways are paired one on each side of the spinal cord

White Matter: Pathway Generalizations

Descending (Motor) Pathways
Descending tracts deliver motor instructions from the brain to the spinal cord Divided into two groups Pyramidal, or corticospinal, tracts Indirect pathways, essentially all others Motor pathways involve two neurons Upper motor neuron (UMN) Lower motor neuron (LMN) aka ‘anterior horn motor neuron” (also, final common pathway)

Pyramidal (Corticospinal) Tracts
Originate in the precentral gyrus of brain (aka, primary motor area) I.e., cell body of the UMN located in precentral gyrus Pyramidal neuron is the UMN Its axon forms the corticospinal tract UMN synapses in the anterior horn with LMN Some UMN decussate in pyramids = Lateral corticospinal tracts Others decussate at other levels of s.c. = Anterior corticospinal tracts LMN (anterior horn motor neurons) Exits spinal cord via anterior root Activates skeletal muscles Regulates fast and fine (skilled) movements

Corticospinal tracts Location of UMN cell body in cerebral cortex
Decussation of UMN axon in pyramids or at level of exit of LMN Synapse of UMN and LMN occurs in anterior horn of s.c. LMN axon exits via anterior root

Extrapyramidal Motor Tracts
Includes all motor pathways not part of the pyramidal system Upper motor neuron (UMN) originates in nuclei deep in cerebrum (not in cerebral cortex) UMN does not pass through the pyramids! LMN is an anterior horn motor neuron This system includes Rubrospinal Vestibulospinal Reticulospinal Tectospinal tracts Regulate: Axial muscles that maintain balance and posture Muscles controlling coarse movements of the proximal portions of limbs Head, neck, and eye movement

Extrapyramidal Tract Note: 1. UMN cell body location 2. UMN axon decussates in pons 3. Synapse between UMN and LMN occurs in anterior horn of sc 3. LMN exits via ventral root 4. LMN axon stimulates skeletal muscle

Extrapyramidal (Multineuronal) Pathways
Reticulospinal tracts – originates at reticular formation of brain; maintain balance Rubrospinal tracts – originate in ‘red nucleus’ of midbrain; control flexor muscles Tectospinal tracts - originate in superior colliculi and mediate head and eye movements towards visual targets (flash of light)

Main Ascending Pathways
The central processes of first-order neurons branch diffusely as they enter the spinal cord and medulla Some branches take part in spinal cord reflexes Others synapse with second-order neurons in the cord and medullary nuclei

Three Ascending Pathways
The nonspecific and specific ascending pathways send impulses to the sensory cortex These pathways are responsible for discriminative touch (2 pt. discrimination) and conscious proprioception (body position sense). The spinocerebellar tracts send impulses to the cerebellum and do not contribute to sensory perception

Nonspecific Ascending Pathway
Include the lateral and anterior spinothalamic tracts Lateral: transmits impulses concerned with pain and temp. to opposite side of brain Anterior: transmits impulses concerned with crude touch and pressure to opposite side of brain 1st order neuron: sensory neuron 2nd order neuron: interneurons of dorsal horn; synapse with 3rd order neuron in thalamus 3rd order neuron: carry impulse from thalamus to postcentral gyrus

Specific and Posterior Spinocerebellar Tracts
Dorsal Column Tract 1. AKA Medial lemniscal pathway 2. Fibers run only in dorsal column 3. Transmit impulses from receptors in skin and joints 4. Detect discriminative touch and body position sense =proprioception 1st O.N.- a sensory neuron synapses with 2nd O.N. in nucleus gracilis and nucleus cuneatus of medulla 2nd O.N.- an interneuron decussate and ascend to thalamus where it synapses with 3rd O.N. 3rd-order (thalamic neurons) transmits impulse to somatosensory cortex (postcentral gyrus) Spinocerebellar Tract Transmit info. about trunk and lower limb muscles and tendons to cerebellum No conscious sensation

Spinal Cord Trauma and Disorders
Severe damage to ventral root results in flaccid paralysis (limp and unresponsive) Skeletal muscles cannot move either voluntarily or involuntarily Without stimulation, muscles atrophy. When only UMN of primary motor cortex is damaged spastic paralysis occurs - muscles affected by persistent spasms and exaggerated tendon reflexes Muscles remain healthy longer but their movements are no longer subject to voluntary control. Muscles commonly become permanently shortened. Transection (cross sectioning) at any level results in total motor and sensory loss in body regions inferior to site of damage. If injury in cervical region, all four limbs affected (quadriplegia) If injury between T1 and L1, only lower limbs affected (paraplegia)

Spinal Cord Trauma and Disorders
Spinal shock - transient period of functional loss that follows the injury Results in immediate depression of all reflex activity caudal to lesion. Bowel and bladder reflexes stop, blood pressure falls, and all muscles (somatic and visceral) below the injury are paralyzed and insensitive. Neural function usually returns within a few hours following injury If function does not resume within 48 hrs, paralysis is permanent. Amyotrophic Lateral Sclerosis (aka, Lou Gehrig’s disease) Progressive destruction of anterior horn motor neurons and fibers of the pyramidal tracts Lose ability to speak, swallow, breathe. Death within 5 yrs Cause unknown (90%); others have high glutamate levels Poliomyelitis Virus destroys anterior horn motor neurons Victims die from paralysis of respiratory muscles Virus enters body in feces-contaminated water (public swimming pools)

The Peripheral Nervous System (PNS) is comprised of the: Somatic Nervous System Autonomic Nervous System

The Somatic Nervous System consists of nerves that: Convey sensory information to the CNS. Transmit messages for motor movement from the CNS to the body.

The autonomic nervous system regulates the automatic behaviors of the body (heart rate, blood pressure, respiration, digestion etc). The autonomic nervous system can be divided into two subsystems: The Sympathetic Nervous System. The Parasympathetic Nervous System.

Figure 4.6: The sympathetic nervous system (red lines) and parasympathetic nervous system (blue lines). Note that the adrenal glands and hair erector muscles receive sympathetic input only. (Source: Adapted from Biology: The Unity and Diversity, 5th Edition, by C. Starr and R. Taggart, p Copyright © 1989 Wadsworth.) Fig. 4-6, p. 86

The sympathetic nervous system is a network of nerves that prepares the organs for rigorous activity: increases heart rate, blood pressure, respiration, etc. (“fight or flight” response) comprised of ganglia on the left and right of the spinal cord mainly uses norepinephrine as a neurotransmitter at the postganglionic synapses.

The parasympathetic nervous system facilitates vegetative, nonemergency responses by the organs. decreases functions increased by the sympathetic nervous system. comprised of long preganglion axons extending from the spinal cord and short postganglionic fibers that attach to the organs themselves. dominant during our relaxed states.

Parasympathetic Nervous System (cont’d) Postganglionic axons mostly release acetylcholine as a neurotransmitter

The brain can be divided into three major divisions: Hindbrain. Midbrain. Forebrain.

The Hindbrain consists of the: Medulla. Pons. Cerebellum. Located at the posterior portion of the brain Hindbrain structures, the midbrain and other central structures of the brain combine and make up the brain stem.

Figure 4.8: The human brainstem.
This composite structure extends from the top of the spinal cord into the center of the forebrain. The pons, pineal gland, and colliculi are ordinarily surrounded by the cerebral cortex.

The medulla: Located just above the spinal cord and could be regarded as an enlarged extension of the spinal cord. responsible for vital reflexes such as breathing, heart rate, vomiting, salivation, coughing and sneezing. Cranial nerves allow the medulla to control sensations from the head, muscle movements in the head, and many parasympathetic outputs to the organs.

Figure 4.9: Cranial nerves II through XII.
Cranial nerve I, the olfactory nerve, connects directly to the olfactory bulbs of the forebrain. (Source: Based on Braus, 1960)

Pons lies on each side of the medulla (ventral and anterior). along with the medulla, contains the reticular formation and raphe system. works in conjunction to increase arousal and readiness of other parts of the brain.

The reticular formation: descending portion is one of several brain areas that control the motor areas of the spinal cord. ascending portion sends output to much of the cerebral cortex, selectively increasing arousal and attention. The raphe system also sends axons to much of the forebrain, modifying the brain’s readiness to respond to stimuli.

The Cerebellum: a structure located in the hindbrain with many deep folds. helps regulate motor movement, balance and coordination. is also important for shifting attention between auditory and visual stimuli.

The midbrain is comprised of the following structures: Tectum – roof of the midbrain Superior colliculus &inferior colliculus– swellings on each side of the tectum and routes for sensory information Tagmentum- the intermediate level of the midbrain Substantia nigra - gives rise to the dopamine-containing pathway

The forebrain is the most anterior and prominent part of the mammalian brain and consists of two cerebral hemispheres Consists of the outer cortex and subcortical regions. outer portion is known as the “cerebral cortex”. Receives sensory information and controls motor movement from the opposite (contralateral) side of the body.

Figure 4.10: A sagittal section through the human brain.
(Source: After Nieuwenhuys, Voogd, & vanHuijzen, 1988) Fig. 4-10, p. 90

Subcortical regions are structures of the brain that lie underneath the cortex. Subcortical structures of the forebrain include: Thalamus - relay station from the sensory organs and main source of input to the cortex. Basal Ganglia - important for certain aspects of movement.

The limbic system consists of a number of other interlinked structures that form a border around the brainstem. Includes the olfactory bulb, hypothalamus, hippocampus, amygdala, and cingulate gyrus of the cerebral cortex associated with motivation, emotion, drives and aggression.

Figure 4.12: The limbic system is a set of subcortical structures that form a border (or limbus) around the brainstem. Fig. 4-12, p. 91

Hypothalamus Small area near the base of the brain. Conveys messages to the pituitary gland to trigger the release of hormones. Associated with behaviors such as eating, drinking, sexual behavior and other motivated behaviors. Thalamus and the hypothalamus together form the “diencephalon”.

Figure 4.14: Routes of information from the thalamus to the cerebral cortex.
Each thalamic nucleus projects its axons to a different location in the cortex. (Source: After Nieuwenhuys, Voogd, & vanHuijzen, 1988) Fig. 4-14, p. 92

Pituitary gland - hormone producing gland found at the base of the hypothalamus. Basal Ganglia - comprised of the caudate nucleus, the putamen and the globus pallidus. Associated with planning of motor movement, and aspects of memory and emotional expression .

Fig. 4-15, p. 93 Figure 4.15: The basal ganglia.
The thalamus is in the center, the basal ganglia are lateral to it, and the cerebral cortex is on the outside. (Source: After Nieuwenhuys, Voogd, & vanHuijzen, 1988) Fig. 4-15, p. 93

Basal forebrain is comprised of several structures that lie on the dorsal surface of the forebrain. Contains the nucleus basalis: receives input from the hypothalamus and basal ganglia sends axons that release acetylcholine to the cerebral cortex Key part of the brains system for arousal, wakefulness, and attention

Fig. 4-16, p. 93 Figure 4.16: The basal forebrain.
The nucleus basalis and other structures in this area send axons throughout the cortex, increasing its arousal and wakefulness through release of the neurotransmitter acetylcholine. (Source: Adapted from “Cholinergic Systems in Mammalian Brain and Spinal Cord,” by N. J. Woolf, Progress in Neurobiology, 37, pp. 475–524, 1991) Fig. 4-16, p. 93

Hippocampus is a large structure located between the thalamus and cerebral cortex. critical for storing certain types of memory.

The central canal is a fluid-filled channel in the center of the spinal cord. The ventricles are four fluid-filled cavities within the brain containing cerebrospinal fluid. Cerebrospinal fluid is a clear fluid similar to blood plasma found in the brain and spinal cord: Provides “cushioning” for the brain. Reservoir of hormones and nutrition for the brain and spinal cord.

Fig. 4-17, p. 94 Figure 4.17: The cerebral ventricles.
(a) Diagram showing positions of the four ventricles. (b) Photo of a human brain, viewed from above, with a horizontal cut through one hemisphere to show the position of the lateral ventricles. Note that the two parts of this figure are seen from different angles. (Photo courtesy of Dr. Dana Copeland) Fig. 4-17, p. 94

The Cerebral Cortex The cerebral cortex is the most prominent part of the mammalian brain and consists of the cellular layers on the outer surface of the brain. comprised of grey matter and white matter. divided into two halves joined by two budndles of axons called the corpus callosum and the anterior commissure. more highly developed in humans than other species.

The Cerebral Cortex Organization of the Cerebral Cortex:
Contains up to six distinct laminae (layers) that are parallel to the surface of the cortex. Cells of the cortex are also divided into columns that lie perpendicular to the laminae. Divided into four lobes: occipital, parietal, temporal, and frontal.

Figure 4.21: The six laminae of the human cerebral cortex.
(Source: From S. W. Ranson and S. L. Clark, The Anatomy of the Nervous System, 1959, Copyright © 1959 W. B. Saunders Co. Reprinted by permission.) Fig. 4-21, p. 97

Fig. 4-22, p. 98 Figure 4.22: Columns in the cerebral cortex.
Each column extends through several laminae. Neurons within a given column have similar properties. For example, in the somatosensory cortex, all the neurons within a given column respond to stimulation of the same area of skin. Fig. 4-22, p. 98

The Cerebral Cortex The four lobes of the cerebral cortex include the following: Occipital lobe Parietal lobe Temporal lobe Frontal lobe

Fig. 4-23, p. 99 Figure 4.23: Areas of the human cerebral cortex.
(a) The four lobes: occipital, parietal, temporal, and frontal. (b) The primary sensory cortex for vision, hearing, and body sensations; the primary motor cortex; and the olfactory bulb, a noncortical area responsible for the sense of smell. (Source for part b: T. W. Deacon, 1990) Fig. 4-23, p. 99

The Cerebral Cortex Occipital lobe:
Located at the posterior end of the cortex. Known as the striate cortex or the primary visual cortex. Highly responsible for visual input. Damage can result in cortical blindness.

The Cerebral Cortex Parietal lobe
Contains the postcentral gyrus (aka “primary somatosensory cortex”) is the primary target for touch sensations, and information from muscle-stretch receptors and joint receptors. Also responsible for processing and integrating information about eye, head and body positions from information sent from muscles and joints.

Figure 4.24: Approximate representation of sensory and motor information in the cortex.
(a) Each location in the somatosensory cortex represents sensation from a different body part. (b) Each location in the motor cortex regulates movement of a different body part. (Source: Adapted from The Cerebral Cortex of Man by W. Penfield and T. Rasmussen, Macmillan Library Reference. Reprinted by permission of The Gale Group.) Fig. 4-24, p. 99

The Cerebral Cortex Temporal Lobe
Located on the lateral portion of the hemispheres near the temples. Target for auditory information and essential for processing spoken language. Also responsible for complex aspects of vision including movement and some emotional and motivational behaviors.

The Cerebral Cortex The Frontal lobe:
Contains the prefrontal cortex and the precentral gyrus. Precentral gyrus is also known as the primary motor cortex and is responsible for the control of fine motor movement. Contains the prefrontal cortex- the integration center for all sensory information and other areasof the cortex. (most anterior portion of the frontal lobe)

Figure 4.25: Species differences in prefrontal cortex.
Note that the prefrontal cortex (blue area) constitutes a larger proportion of the human brain than of these other species. (Source: After The Prefrontal Cortex by J. M. Fuster, 1989, Raven Press. Reprinted by permission.) Fig. 4-25, p. 100

The Cerebral Cortex The Prefrontal cortex (cont’d)
responsible for higher functions such as abstract thinking and planning. responsible for our ability to remember recent events and information (“working memory”). allows for regulation of impulsive behaviors and the control of more complex behaviors.

The Cerebral Cortex Various parts of the cerebral cortex do not work independently of each other. All areas of the brain communicate with each other The binding problem refers to the question of how the visual, auditory, and other areas of the brain produce a perception of a single object. perhaps the brain binds activity in different areas when they produce synchronous waves of activity

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