Neuroanatomy: Spinal Cord, Reflexes, and Autonomic NS

Major Regions of the Brain

• Cerebrum is the largest component, controlling higher mental functions like thought and intellect
• Divided into two hemispheres (left and right) separated by the longitudinal fissure
• Connected by the corpus callosum
• Diencephalon includes the midbrain, pons, and medulla oblongata
• Cerebellum is involved in coordination and balance

Cerebrum Structure

• Gray matter forms a thin outer layer, known as the cerebral cortex
• Contains neuron cell bodies
• White matter is located internally and contains nerve fibers
• Cerebral nuclei (basal nuclei) are areas of gray matter within the white matter

Cerebral Hemispheres

• Frontal lobe is located at the front of the forehead, bordered by the precentral gyrus
• Parietal lobe is located towards the middle of the head, bordered by the postcentral gyrus and the parieto-occipital sulcus
• Temporal lobe is situated in the middle bottom of the brain
• Occipital lobe is located at the back of the head, bordering the parieto-occipital sulcus
• Sulci are shallow depressions, and gyri are elevated ridges that increase the surface area of the cortex

Functional Areas of the Cerebrum

• Each hemisphere receives sensory information from the opposite side of the body and sends motor commands to the opposite side
• Motor cortices, located in the precentral gyrus of the frontal lobe, direct voluntary movements
• Primary sensory cortex, located in the postcentral gyrus of the parietal lobe, receives somatic sensory information (e.g., touch, pressure, pain, temperature)
• Special sensory cortices include the visual cortex (occipital lobe), auditory cortex (temporal lobe), olfactory cortex (temporal lobe), and gustatory cortex (frontal lobe)
• Association areas are located adjacent to sensory and motor areas, coordinating learned movements and interpreting sensory information

Higher Order Centres (Association Areas)

• Integrative centers receive input from multiple association areas
• They coordinate complex motor or analytical activities, including speech and pre-frontal cortex functions

General Interpretive Area (GIA)

• Also known as Wernicke's area, typically found in the left hemisphere
• Receives information from all sensory association areas
• Coordinates access to complex visual and auditory memories

Hemispheric Lateralization

• The dominant hemisphere (usually the left) handles language-related tasks (e.g., speech, writing, mathematics)
• The non-dominant hemisphere is involved in spatial visualization and analysis

Basal Nuclei (Cerebral Nuclei)

• Masses of gray matter embedded in the white matter of the cerebrum
• Involved in subconscious control of skeletal muscle tone and coordination of learned movement patterns

Limbic System

• Functional group of tracts between the cerebrum and diencephalon
• Establishes emotional states, facilitates memory storage and retrieval & motivates actions

Diencephalon

• Integrates sensory information and motor commands
• Consists of the epithalamus, thalamus, and hypothalamus

Epithalamus

• Forms the root of the diencephalon
• Anterior part contains choroid plexus
• Posterior part contains pineal gland (melatonin)

Thalamus

• Round mass of thalamic nuclei
• Relay point for sensory information (except smell)

Hypothalamus

• Located below the thalamus, above the pituitary gland
• Contains important control and integrative centers
• Regulates autonomic functions, endocrine system, and emotional responses
• Controls body temperature and circadian cycles

Brain Stem

• Midbrain, pons, and medulla oblongata
• Connects the brain to the spinal cord
• Contains autonomic centers (e.g., respiratory, vasomotor)
• Includes relay centers for sensory and motor pathways

Cerebellum

• Second largest part of the brain
• Has two hemispheres connected by the vermis
• Involved in adjusting postural muscles, maintaining balance, and coordinating and smoothing voluntary and involuntary movements

The Meninges

• Three layers of protective membranes (dura mater, arachnoid mater, pia mater):
• Protects and supports the brain and spinal cord
• Contains cerebrospinal fluid for cushioning

Ventricles of the Brain

• Four internal cavities containing cerebrospinal fluid (CSF)
• Interconnected channels

Cerebrospinal Fluid (CSF)

• Clear, watery fluid surrounding CNS
• Produced by choroid plexuses in the ventricles
• Circulates through the ventricles and subarachnoid space
• Provides cushioning and protection

Blood Supply of the Brain

• Highly active organ supplied by internal carotid arteries and vertebral arteries

Spinal Cord

• Conus medullaris
• Cauda equina
• Consist of 31 segments (8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal)

Spinal Cord Structure

• Posterior median sulcus
• Anterior median fissure
• Central canal filled with CSF

Spinal Segments

• Dorsal roots contain sensory axons
• Dorsal root ganglia contain sensory neuron cell bodies
• Ventral roots contain motor axons
• Spinal nerves are formed by the fusion of dorsal and ventral roots

Nerve Plexuses

• Networks of major nerve trunks
• Cervical, brachial, lumbar, and sacral (lumbosacral) plexuses

Reflexes

• Rapid, automatic motor responses to stimuli
• Usually involve a sensory receptor, sensory neuron, processing within the CNS, a motor neuron, and an effector
• Simple (monosynaptic) or complex (polysynaptic) reflexes

Autonomic Nervous System (ANS)

• Controls involuntary functions such as heart rate, digestion, and respiration
• Has two divisions: sympathetic (fight-or-flight) and parasympathetic (rest-and-digest)

Ascending and Descending Pathways

• Ascending pathways carry sensory information to the brain
• Descending pathways carry motor commands from the brain to the body

Circle of Willis

• Arterial ring on the ventral surface of the brain
• Connects internal carotid and vertebrobasilar systems
• Provides alternative routes for blood flow

Venous Drainage of the Brain

• Veins drain into dural venous sinuses and eventually into the internal jugular veins.