Brain
Evolution of the Brain
Brain Components
Three main regions based on location:
- The Forebrain (Prosencephalon) - Front and upper regions, responsible for higher-level functions
- Cerebrum - Two hemispheres, each covered by the cerebral cortex, which is responsible for complex cognitive functions. Separated into four lobes from front to back:
- Frontal Lobe - Responsible for planning, decision-making, voluntary movement, language (Broca's area), and personality (Frontal Lobe)
- Parietal Lobe - Processes sensory information such as touch, temperature, pain, and spatial awareness (Parietal Lobe
- Temporal Lobe - Primarily involved in hearing, memory, language (Wernicke's area), and processing emotions (Temporal Lobe
- Hippocampus - Memory formation (Hippocampus
- Amygdala - Emotions (Amygdala
- Occipital Lobe - Processing visual information (Occipital Lobe)
- Corpus callosum - Bundle of nerve fibres connecting the two hemispheres (Corpus callosum)
- Diencephalon - Situated beneath the cerebrum (Diencephalon):
- Thalamus - A relay station for sensory and motor information going to and from the cerebral cortex. Also plays a role in consciousness, sleep, and alertness (Thalamus)
- Hypothalamus - Regulates bodily functions like temperature, hunger, thirst, sleep-wake cycles, and hormone release. Connects the nervous system to the endocrine system via the pituitary gland (Hypothalamus)
- Pineal Gland - regulates sleep-wake cycles through the secretion of melatonin. (Pineal Gland)
- Cerebrum - Two hemispheres, each covered by the cerebral cortex, which is responsible for complex cognitive functions. Separated into four lobes from front to back:
- The Midbrain (Mesencephalon) - Located beneath the forebrain, acts as a relay center for sensory and motor information and plays a role in motor control, vision, hearing, and sleep-wake cycles.
- Superior colliculi - Controls head movements in reponse to visual input and coordinates eye movements (Superior colliculi)
- Inferior colliculi - Controls head movements in reponse to auditory input (Inferior colliculi)
- Substantia nigra - Motor function (Substantia nigra)
- The Hindbrain (Rhomencephalon) - Located at the bak and lower part of the brain, connecting to the spinal cord, crucial for many basic life functions:
- Cerebellum - Behind the brainstem, responsible for coordinating voluntary movement, posture, balance, and motor learning (Cerebellum)
- Brainstem - Connects the cerebrum and cerebellum to the spinal cord:
- Pons - regulates breathing, plays roles in sleep and facial expressions (Pons)
- Medulla Oblongate - controls heart rate, breathing, blood pressure and relexes like vomiting, coughing, and swallowing (Medulla Oblongate)
- Cerebral Hemispheres/Cerebral Cortex - concerned with higher mental functions: perception, action, language, and planning. Contains about 100 billion neurons, each with about a thousand synapses, making a total of about 100 trillion synaptic connections
- Frontal lobe - part of the neural circuit governing social judgements, planning and organization of activities, aspects of language, control of movement, and a form of short-term memory called working memory
- Parietal lobe - receives sensory information about touch, pressure, and space around the body and helps integrate that information into coherent perceptions
- somatosensory cortex - a strip in the parietal lobe contains Wilder Penfield's sensory homunculus.
- Occipital lobe in involved in vision
- Temporal lobe is involved with auditory processing and aspects of language and memory.
- Basal ganglia - help regulate motor performance
- Hippocampus - involved with aspects of memory storage
- Amygdala - coordinates autonomic and endocrine responses in the context of emotional states
Brain Functions
The brain provides coherent control over the actions of an animal. Information from the sense organs is collected in the brain, where it is processed to extract information about the structure of the environment. It combines the processed information with info about the current needs of the animal and with memory of past circumstances, and then generates motor responses. The main functions are:
- Perception - The brain collects info from the senses.
- Motor control - Motor systems are areas of the brain, mainly in the spinal cord and hindbrain, that initiate body movements by activating muscles.
- Sleep - The brain controls the transitions from sleeping to waking in a daily cycle
- Homeostasis - maintaining parameters (such as temperature, water content, salt concentration in the bloodstream, blood glucose levels, blood oxygen level) within a limited range of variation, through negative feedback
- Motivation - The brain activates behaviors to meet any needs that arise, generally through a reward-punishment mechanism. The basal ganglia inihibit most of the motor systems in the brain, and then release the inhibition for a specific motor system to allow its action to be carried out.
- Learning and memory - modifying behavior based on experience:
- Working memory - maintaining a temporary representation of information about the task that you are currently working on
- Episodic memory - remembering the details of specific events. The Hippocampus is heavily involved.
- Semantic memory - remembering facts and relationships. Mainly in the Cerebral Cortex
- Instrumental learning - allowing rewards and punishments to modify behavior
- Motor learning - refining patterns of body movement by practicing or repetition