Sensory Pathways | Touch/Proprioception vs Pain/Temperature

Summary

In this educational video, Dr. Mike explains the process by which sensations from the hand or feet are transmitted to the brain. He details how fine touch receptors send signals up the spinal cord, synapsing at the medulla before crossing to the opposite side and reaching the thalamus, the brain's sorting center. Here, a third neuron relays the touch information to the hand's cortical representation. Pain signals, however, cross immediately upon entering the spinal cord, bypassing the brain stem but still reaching the thalamus, indicating the brain's prioritization of pain awareness. The explanation highlights the complexity of sensory pathways and their implications in spinal cord injuries, such as Brown-Séquard syndrome.

Takeaways

• 👋 Sensation from the hand is initiated by receptors that detect touch and transmit signals to the spinal cord.
• 🔁 The signal for fine touch travels up the same side of the spinal cord from which it originated.
• 🌟 The brain stem, consisting of the midbrain, pons, and medulla, is where the first signal synapses and the second neuron crosses to the opposite side.
• 🔄 The second neuron's crossing over is crucial for the transmission of sensory information to the opposite side of the brain.
• 📮 The thalamus acts as the brain's sorting center, directing sensory information to the appropriate areas of the cortex.
• 🧠 The cortex is responsible for awareness; without signals reaching it, we remain unaware of sensations.
• 🤲 The hand has a large area dedicated in the cortex due to its sensitivity, indicating the brain's detailed mapping of the body.
• 💉 Pain signals from the hand, such as from a pinprick, also travel to the spinal cord but synapse and cross over immediately upon entry.
• 🚫 Pain signals bypass the brain stem but are still routed through the thalamus to the brain's pain processing area.
• 🔄 The distinction between fine touch and pain signals is evident in how they travel up the spinal cord—fine touch on the same side and pain on the opposite.
• 🩺 Understanding these pathways is important for diagnosing conditions like Brown-Séquard syndrome, which involves spinal cord injuries affecting sensory perception differently on each side of the body.

Q & A

What is the purpose of the video by Dr. Mike?

The purpose of the video is to explain how sensations, such as touch and pain, are transmitted from the hand or feet to the brain via the spinal cord.

What receptors are stimulated when someone tickles your hand?

Fine touch receptors in the hand are stimulated, which pick up the gentle soft touch and transmit a signal to the brain.

How does the signal from the hand travel to the brain?

The signal travels down the arm, enters the spinal cord, and goes up the same side of the spinal cord until it reaches the brain stem.

What part of the brain does the signal first synapse with after reaching the brain stem?

The signal first synapses at the medulla, which is part of the brain stem, with another neuron.

What is the role of the thalamus in the process of sensation transmission?

The thalamus acts as the sorting center of the brain, where all information from the body that wants to reach the conscious brain must pass through.

How is the area of the brain dedicated to the hand represented?

The hand is represented by a large area on the cortex of the brain, which is mapped according to the sensitivity of different body parts.

What happens if the signal does not reach the cortex?

If the signal does not reach the cortex, the person will not be aware of the sensation, as the cortex is responsible for conscious awareness.

How does the transmission of pain differ from the transmission of fine touch?

Pain signals synapse at the spinal cord and cross over to the other side immediately upon entering, while fine touch signals go up to the brain stem before crossing over.

Why is it significant that fine touch and pain travel on opposing sides of the spinal cord?

This is significant for understanding the effects of spinal cord injuries, such as hemisection or lesions, which can result in different sensory effects due to damage to one side of the spinal cord.

What is Brown-Séquard syndrome, and how is it related to the script's content?

Brown-Séquard syndrome is a condition resulting from damage to one side of the spinal cord, leading to different sensory and motor effects on the opposite side of the body, which is discussed in the context of the script.

Why does the video mention that pain is always processed by the thalamus?

The video mentions this because pain signals must always reach the thalamus to be sorted and then sent to the appropriate area of the brain, ensuring the person is aware of the painful experience.