Exploring the Endocrine System

The Endocrine System

• The endocrine system is a network of glands producing hormones that regulate metabolism, growth, and sexual development.
• It works closely with the nervous system, especially the limbic system, to regulate thoughts, emotions, and behaviours.
• Main glands include the thyroid (regulates body temperature and heart rate), adrenals (regulate stress responses), pancreas (controls digestion), and pineal (influences the sleep-wake cycle via melatonin).
• The pituitary gland orchestrates the endocrine system by directing the functions of other glands

Hormonal Signals and Stress Response

• The hypothalamus sends hormonal signals to the pituitary gland, which then signals other glands to control stress, digestion, and reproduction.
• When a threat is sensed, sensory neurons signal the hypothalamus to release ACTH from the pituitary gland.
• ACTH stimulates the adrenal glands to release hormones that activate the sympathetic nervous system
• This prepares the body to confront the threat or flee.

Sex Hormones

• Ovaries in females produce estrogen, and testes in males produce testosterone
• The ovaries generate small amounts of testosterone, and the testes generate small amounts of estrogen

Sexual Desire

• Research indicates a weak correlation between testosterone levels and sexual desire in both men and women.
• There is evidence for a link between estrogen levels and sexual desire in women

The Cerebral Cortex

• The cortex is the highest level of the brain
• It is responsible for complex perception, emotion, movement, and thought
• It sits over the rest of the brain and is the wrinkled surface seen when looking at the brain

Gyri and Sulci

• Gyri are the smooth, raised surfaces of the cortex.
• Sulci are the indentations or fissures

Organization Across Hemispheres

• The cortex is divided into left and right hemispheres that are symmetrical in appearance and functions.
• Each hemisphere controls the opposite side of the body, known as contralateral control
• Hemispheres communicate via commissures, with the corpus callosum being the largest
• The corpus callosum connects large areas of the cerebral cortex on each side of the brain and supports communication of information across the hemispheres

Organization Within Hemispheres

• Each hemisphere is divided into four lobes: occipital, parietal, temporal, and frontal.
• The occipital lobe, at the back of the cortex, processes visual information.
• Damage to the occipital lobe can cause partial or complete blindness.
• The parietal lobe, in front of the occipital lobe, processes touch information and contains the somatosensory cortex

Somatosensory Cortex

• The somatosensory cortex represents the skin areas on the contralateral surface of the body.
• More sensitive body areas have larger parts of the somatosensory cortex devoted to them.
• The homunculus is a distorted figure illustrating the representation of the body in the somatosensory cortex

Motor Cortex

• The motor cortex, in the frontal lobe, initiates voluntary movements.
• Different parts of the motor cortex correspond to different body parts
• The motor and somatosensory cortices act as sending and receiving areas of the cerebral cortex

Temporal Lobe

• The temporal lobe, on the lower side of each hemisphere, is responsible for hearing and language.
• The primary auditory cortex receives sensory information from the ears based on sound frequencies.
• The temporal lobe interprets the meaning of visual stimuli and helps in recognizing common objects

Frontal Lobe

• The frontal lobe, behind the forehead, has specialized areas for movement, abstract thinking, planning, memory, and judgement.
• It contains the motor cortex and coordinates thought processes for manipulating information and retrieving memories
• The frontal cortex functions as an executive for thinking, imagining, planning, and anticipating.

Organization Within Specific Lobes

• Primary areas handle fine details of information, which then go to association areas that provide meaning.
• Association areas interpret information from primary areas to make sense of what is perceived.
• Example visual processing moves from detecting shapes and motion to understanding a threatening situation

Mirror Neuron System

• Mirror neurons activate when an animal performs a behavior and when another animal observes that behavior.
• Mirror neurons are found in the frontal and parietal lobes.
• They are related to recognizing the goal and outcome of an action.

Controversy around Mirror Neurons

• The interpretation of mirror neuron activity, especially in humans, is debated.
• Some suggest that impairments in the mirror neuron system may contribute to difficulties in understanding others' minds, as in autism spectrum disorder.

Neuron Specialization

• Neurons in association areas are less specialized and more flexible than those in primary areas.
• These neurons can be shaped by learning and experience, demonstrating the brain's plasticity.

Brain Plasticity and Sensory Cortices

• Sensory cortices are adaptable to changes in sensory inputs, a quality known as plasticity.
• For example, the cortical area representing a lost finger becomes unresponsive initially.

Phantom Limb Syndrome

• Amputees experience sensations where the missing limb would be, known as phantom limb syndrome.
• Brain scans of amputees show that stimulating the face and upper arm activates an area in the somatosensory cortex that previously would have been activated by the missing hand

Brain Plasticity and Cortical Reorganization

• The cortical representations for the face and upper arm take over the part of the cortex normally representing the hand
• New face and arm representations become contiguous, filling in the space occupied by the hand representation

Influence of Practice on Brain Plasticity

• Stimulation of one finger can lead to that finger "taking over" the representation of adjacent fingers in the cortex.
• Concert pianists have highly developed cortical areas for finger control due to continued input from the fingers
• Professional musicians show greater plasticity within the motor cortex compared to nonmusicians, possibly due to increased motor synapses from practice

Physical Exercise and Brain Plasticity

• Physical exercise can increase the number of synapses and promote the development of new neurons in the hippocampus
• Cardiovascular exercise has beneficial effects on brain function and cognitive performance
• Even a single session of moderate-to-intensive exercise can boost aspects of memory and motor skills
• Activity-dependent brain plasticity is relevant to treating spinal cord injuries by maximizing plasticity through exercise and training

Culture and Brain Plasticity

• Cultural psychology and neuroscience studies show that culture impacts neurobiological processes.
• Westerners tend to focus more on the focal object where as Easterners tend to focus more on the background information
• The Cognitive differences are accompanied by differing neural responses in visual cortex to objects and backgrounds
• Evidence for cultural differences in cognitive and neural responses highlights again that the brain is plastic and that culture plays a key role in its wiring

Alzheimer's Disease (AD) and the Hippocampus

• Alzheimer's disease (AD) gradually impairs memory and cognitive functions.
• AD is more prevalent among women than men worldwide.
• The hippocampus, critical for learning and memory, shows potentially important sex differences

Hippocampal Volume and AD

• Hippocampal volume is reduced in AD patients compared to cognitively intact older adults.
• Hippocampal atrophy progresses about 1.5 times faster in women than in men.
• Changes in hippocampal volume over time are more predictive of an eventual AD diagnosis in women than in men

Sex Differences in AD

• Women exhibit greater rates of brain atrophy in several regions and faster cognitive decline compared to men.
• These sex differences have implications for diagnosis and treatment of AD
• Investigating sex differences to craft sex-specific approaches to diagnosis and treatment