Neuroscience Chapter: The Forebrain and Subcortex

The Forebrain (Telencephalon)

• The parietal lobes contain the primary somatosensory cortex (S1), which is responsible for touch, pressure, pain, and temperature sensations.
• The parietal lobes also contain a homunculus, a representation of the body in the brain.
• Proprioception is the ability to know the relative position of one's body parts, and is also processed in the parietal lobe.
• The temporal lobes contain the primary auditory cortex, and Wernicke's area, which is important for understanding language.
• Information about language acquired by Wernicke's area is relayed to Broca's area for the proper production of speech.
• Damage to Wernicke's area can cause Wernicke's aphasia, a condition which makes it difficult to understand language.
• The temporal lobes are also important for memory and the recognition of objects.
• The occipital lobes contain the primary visual cortex (V1), where visual information is first analyzed.

Subcortical Structures

• The Basal Ganglia consists of several nuclei, including the dorsal striatum, ventral striatum, and substantia nigra.
• The Basal Ganglia play a role in smooth execution of movement and the selection of appropriate actions.
• The Basal Ganglia are also involved in habit learning.
• Parkinson's disease affects the Basal Ganglia.
• In Parkinson's disease, neurons in the substantia nigra die, depriving the dorsal striatum of dopaminergic inputs.
• The Hippocampus is critical for memory.
• Damage to the hippocampus can lead to difficulties in acquiring, storing, and retrieving certain types of memories.
• The hippocampus is important for spatial navigation and spatial learning.
• The Amygdala is deeply interconnected with the hippocampus and plays a role in emotional processing.
• Damage to the amygdala can cause emotional dysregulation.

The Diencephalon

• The Thalamus acts as a relay station for sensory information between receptors and the brain areas responsible for interpreting those sensations.
• The Thalamus is also critical for movement and the regulation of sleep-wake cycles.
• The Hypothalamus regulates many of the body's functions, and is a major player in homeostasis, the maintenance of a stable internal environment.

The Midbrain and Hindbrain

• The Tectum, a part of the midbrain, is subdivided into two areas: the superior colliculus and the inferior colliculus.
• The superior colliculus is also known as the optic tectum, because it plays an important role in controlling eye movements.
• The inferior colliculus processes auditory information.
• The Tegmentum, another part of the midbrain, is important for movement and reward; it houses the substantia nigra and the ventral-tegmental area.
• The Cerebellum, part of the hindbrain, is important for motor coordination.
• Damage to the Cerebellum can lead to difficulties in adjusting ongoing movements and coordinating limbs.

The Spinal Cord

• The Spinal Cord is a pathway for transmitting information and signals between the brain and the peripheral nervous system.
• Paraplegia is the loss of use and sensation in the lower limbs, caused by damage to the lower parts of the spinal cord.
• Quadriplegia (also known as tetraplegia) is the loss of use and sensation in both upper and lower limbs, resulting from damage to the upper spinal cord.

The Protected Brain

• The Meninges are three membranes that envelop the brain and spinal cord: the pia mater, the arachnoid mater, and the dura mater.
• Cerebrospinal Fluid cushions the brain and spinal cord.
• The Blood-Brain Barrier is a protective barrier formed by the cells of the brain's blood vessels, which block or slow the passage of harmful molecules to the brain.

Hemispheric Specialization

• The Corpus Callosum is a thick bundle of nerve fibers used to send information from one hemisphere to the other.
• Hemispheric Asymmetry refers to the fact that some functions are associated with either the right or left hemisphere of the brain.

Cerebral Dominance

• Broca observed a relationship between handedness and the speech area of the brain.
• The hemisphere that contained the language area became known as the dominant hemisphere.
• Split-Brain Patients have had the corpus callosum removed.

The Peripheral Nervous System (PNS)

• The PNS consists of the parts of the nervous system outside the central nervous system.
• The Somatic Nervous System (SNS) is responsible for voluntary control of movement.
• The SNS consists of nerve fibers that enter and exit the spinal cord.
• Sensory neurons convey sensory information from the skin, muscles, joints, tendons, blood vessels, and organs.
• Sensory neurons (afferent neurons) enter the back of the spinal cord through the dorsal roots.
• Motor neurons (efferent neurons) move muscles and exit the front of the spinal cord through the ventral roots.
• The Patellar Reflex is a reflex arc that starts with the activation of sensory neurons and ends with muscle contraction.
• The CNS and PNS are functionally and physiologically interrelated.

The Autonomic Nervous System (ANS)

• The ANS controls involuntary muscles.
• The Sympathetic Nervous System prepares the body for action, known as the "fight-or-flight" response.
• The Parasympathetic Nervous System slows things down, known as the "rest-and-digest" response.
• Ganglia are collections of cell bodies.
• Preganglionic fibers exit the spinal cord and enter ganglia.
• Postganglionic fibers exit ganglia and enter the spinal cord.

The Cranial Nerves

• The Cranial Nerves are 12 pairs, each with a name and number.
• Some cranial nerves transmit information from the senses.
• Other cranial nerves are involved in movement.
• The Vagus Nerve is the cranial nerve with the most complex set of connections.
• The Vagus Nerve plays an important role in the PNS, slowing the heart, regulating internal organs, and controlling muscles involved in speech.