The brain's intricate structure is key to understanding behavior and cognition. From the cerebral cortex to the brainstem, each region plays a unique role in processing information and controlling bodily functions.

Neuroanatomy reveals how different brain areas work together to produce complex behaviors. By examining major structures and their functions, we gain insight into how the nervous system operates and how damage can lead to specific disorders.

Brain Regions and Functions

Forebrain Structures and Functions

• The forebrain is the largest region of the brain and includes the cerebral cortex, which is divided into four lobes:
  • Frontal lobe: involved in executive functions, decision-making, and motor control
  • Parietal lobe: processes sensory information related to touch, pressure, and proprioception
  • Temporal lobe: involved in auditory processing, language comprehension, and memory formation
  • Occipital lobe: primarily responsible for visual processing
• The forebrain also contains several subcortical structures:
  • Thalamus: acts as a relay station for sensory information, directing it to the appropriate cortical areas for processing
  • Hypothalamus: regulates homeostasis by controlling body temperature, hunger, thirst, and endocrine function via the pituitary gland
  • Basal ganglia: a group of nuclei involved in motor control, learning, and execution of complex motor patterns (Parkinson's disease)

Midbrain and Hindbrain Structures and Functions

• The midbrain is a small region that connects the forebrain to the hindbrain and serves as a relay station for sensory and motor information
  • Contains nuclei involved in auditory and visual processing (superior and inferior colliculi)
  • Plays a role in motor coordination and control of eye movements
• The hindbrain includes several important structures:
  • Cerebellum: involved in motor coordination, balance, and fine-tuning of movements (ataxia)
  • Pons: acts as a relay station between the cerebral cortex and the cerebellum, and is involved in sleep regulation and arousal
  • Medulla oblongata: contains vital centers that regulate autonomic functions such as breathing, heart rate, and blood pressure (respiratory depression, bradycardia)

Spinal Cord Organization and Functions

Spinal Cord Structure and Segmentation

• The spinal cord is a long, thin bundle of nervous tissue that extends from the brainstem to the lower back, serving as a conduit for sensory and motor information between the brain and the body
• It is organized into segments, with each segment corresponding to a pair of spinal nerves that innervate specific regions of the body (cervical, thoracic, lumbar, sacral)
• The spinal cord is composed of gray matter and white matter:
  • Gray matter contains cell bodies of neurons and is divided into the dorsal (posterior) horn, which receives sensory input, and the ventral (anterior) horn, which contains motor neurons
  • White matter consists of myelinated axons that ascend (carrying sensory information to the brain) or descend (carrying motor commands from the brain)

Spinal Cord Functions and Reflexes

• The spinal cord is involved in transmitting sensory information from the body to the brain and motor commands from the brain to the muscles
• It also plays a crucial role in spinal reflexes, which are rapid, involuntary responses to stimuli that do not require input from the brain
  • Examples of spinal reflexes include the knee-jerk reflex (patellar tendon reflex) and the withdrawal reflex (pulling away from a painful stimulus)
• Spinal reflexes are mediated by simple neural circuits within the spinal cord, involving sensory neurons, interneurons, and motor neurons
• Damage to the spinal cord can result in loss of sensation, paralysis, and impaired reflexes below the level of the injury (spinal cord injury)

Cerebellum's Role in Motor Control

Cerebellum's Inputs and Integration

• The cerebellum is a large structure located at the back of the brain, beneath the occipital lobe of the cerebral cortex
• It receives sensory input from various sources:
  • Vestibular system: provides information about balance and spatial orientation
  • Proprioceptive information: sensory feedback from muscles and joints about body position and movement
  • Cerebral cortex: sends information about planned movements to the cerebellum
• The cerebellum integrates these inputs to fine-tune motor output, ensuring smooth, coordinated, and accurate movements

Cerebellum's Functions and Disorders

• The cerebellum is primarily involved in motor control, coordination, and balance
  • It helps maintain posture, equilibrium, and smooth execution of voluntary movements
• The cerebellum also plays a role in motor learning, allowing individuals to acquire new motor skills and adapt to changes in the environment through practice and repetition (learning to ride a bicycle, playing a musical instrument)
• Damage to the cerebellum can lead to various impairments:
  • Ataxia: impaired coordination and balance, leading to unsteady gait and difficulty with fine motor tasks
  • Dysmetria: inability to control the range of movement, resulting in overshooting or undershooting targets
  • Dysdiadochokinesia: difficulty performing rapid alternating movements, such as tapping fingers or rotating wrists
• Cerebellar disorders can arise from various causes, including stroke, tumors, neurodegeneration (spinocerebellar ataxia), and alcohol-related damage (Wernicke-Korsakoff syndrome)

Brainstem Functions in Vital Regulation

Medulla Oblongata and Pons

• The brainstem is a critical region that connects the cerebral cortex to the spinal cord and consists of the midbrain, pons, and medulla oblongata
• The medulla oblongata contains vital centers that regulate autonomic functions:
  • Respiratory center: controls breathing rate and depth
  • Cardiovascular center: regulates heart rate and blood pressure
  • Digestive center: controls reflexes such as swallowing, vomiting, and peristalsis
• These centers receive input from sensory receptors and adjust autonomic output accordingly to maintain homeostasis
• The pons serves as a relay station between the cerebral cortex and the cerebellum, and also contains nuclei involved in sleep, arousal, and respiratory control (pneumotaxic center)

Midbrain and Reticular Formation

• The midbrain contains nuclei involved in visual and auditory processing, as well as motor coordination
  • Superior colliculus: involved in visual processing and control of eye movements (saccades)
  • Inferior colliculus: involved in auditory processing and reflexive responses to sound
• The substantia nigra, a key structure in the midbrain, is involved in reward processing and motor control
  • Degeneration of dopaminergic neurons in the substantia nigra is associated with Parkinson's disease, leading to motor symptoms such as tremor, rigidity, and bradykinesia
• The reticular formation extends throughout the brainstem and is involved in arousal, attention, and sleep-wake regulation
  • It receives input from various sensory systems and projects widely to the cerebral cortex, influencing cortical activity and awareness
  • Damage to the reticular formation can result in disorders of consciousness, such as coma or persistent vegetative state